Resolve most of warnings present when compiling

Most of these address unused code, missing documentation, etc.
However, many deprecated functions needed replaced in chrono::NaiveDate. This has been done for all applicable locations
Some warnings still present, but those can be dealt with later
Only warnings left when compiling (rust 1.60) are as follows:
warning: use of deprecated associated function `zip::ZipWriter::<W>::start_file_from_path`: by stripping `..`s from the path, the meaning of paths can change. Use `start_file` instead.
  --> util/src/zip.rs:43:21
   |
43 |             writer.get_mut().start_file_from_path(x, options)?;
   |                              ^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: use of deprecated associated function `zip::read::ZipFile::<'a>::sanitized_name`: by stripping `..`s from the path, the meaning of paths can change.
                         `mangled_name` can be used if this behaviour is desirable
  --> util/src/zip.rs:63:31
   |
63 |                 let path = dest.join(file.sanitized_name());
   |                                           ^^^^^^^^^^^^^^

warning: use of deprecated associated function `zip::read::ZipFile::<'a>::sanitized_name`: by stripping `..`s from the path, the meaning of paths can change.
                         `mangled_name` can be used if this behaviour is desirable
   --> util/src/zip.rs:151:24
    |
151 |             let san_name = file.sanitized_name();
    |                                 ^^^^^^^^^^^^^^

warning: `epic_util` (lib) generated 3 warnings
warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
   --> keychain/src/extkey_bip32.rs:338:41
    |
338 |             Error::Ecdsa(ref e) => error::Error::description(e),
    |                                                  ^^^^^^^^^^^
    |
    = note: `#[warn(deprecated)]` on by default

warning: `epic_keychain` (lib) generated 1 warning
warning: unused doc comment
  --> core/src/core/id.rs:77:1
   |
77 | / /// We want to sort short_ids in a canonical and consistent manner so we can
78 | | /// verify sort order in the same way we do for full inputs|outputs|kernels
79 | | /// themselves.
   | |_--------------^
   |   |
   |   rustdoc does not generate documentation for macro invocations
   |
   = note: `#[warn(unused_doc_comments)]` on by default
   = help: to document an item produced by a macro, the macro must produce the documentation as part of its expansion

warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
  --> core/src/core/foundation.rs:50:68
   |
50 |         Err(why) => panic!("Couldn't create {}: {}", path.display(), why.description()),
   |                                                                          ^^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: `epic_core` (lib) generated 2 warnings
   Compiling epic v3.4.0 (/home/biz/EpicCash/epic-warnings)
warning: value assigned to `prev_header` is never read
   --> chain/src/store.rs:516:14
    |
516 |                     let mut prev_header = None;
    |                             ^^^^^^^^^^^
    |
    = note: `#[warn(unused_assignments)]` on by default
    = help: maybe it is overwritten before being read?

warning: value assigned to `prev_header` is never read
   --> chain/src/store.rs:759:14
    |
759 |                     let mut prev_header = None;
    |                             ^^^^^^^^^^^
    |
    = help: maybe it is overwritten before being read?

warning: `epic_chain` (lib) generated 2 warnings
warning: use of deprecated struct `cursive::view::ScrollBase`: `ScrollBase` is being deprecated in favor of the view::scroll module.
  --> src/bin/tui/table.rs:70:21
   |
70 | use cursive::view::{ScrollBase, View};
   |                     ^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: use of deprecated struct `cursive::view::ScrollBase`: `ScrollBase` is being deprecated in favor of the view::scroll module.
   --> src/bin/tui/table.rs:150:14
    |
150 |     scrollbase: ScrollBase,
    |                 ^^^^^^^^^^

warning: use of deprecated struct `cursive::view::ScrollBase`: `ScrollBase` is being deprecated in favor of the view::scroll module.
   --> src/bin/tui/table.rs:176:16
    |
176 |             scrollbase: ScrollBase::new(),
    |                         ^^^^^^^^^^

warning: variant is never constructed: `PowDifficulty`
  --> src/bin/tui/mining.rs:44:2
   |
44 |     PowDifficulty,
   |     ^^^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default
note: `StratumWorkerColumn` has a derived impl for the trait `Clone`, but this is intentionally ignored during dead code analysis
  --> src/bin/tui/mining.rs:39:16
   |
39 | #[derive(Copy, Clone, PartialEq, Eq, Hash)]
   |                ^^^^^
   = note: this warning originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: variant is never constructed: `SecondaryScaling`
   --> src/bin/tui/mining.rs:111:2
    |
111 |     SecondaryScaling,
    |     ^^^^^^^^^^^^^^^^
    |
note: `DiffColumn` has a derived impl for the trait `Clone`, but this is intentionally ignored during dead code analysis
   --> src/bin/tui/mining.rs:105:16
    |
105 | #[derive(Copy, Clone, PartialEq, Eq, Hash)]
    |                ^^^^^
    = note: this warning originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: `epic` (bin "epic") generated 5 warnings
EpicCash / epic

Resolve most of warnings present when compiling #99
