Allow multiple modules to be run from a single binary

[meyer9]

We want to be able to run the beacon, shard, and validator modules all from the same binary.

TODO:

• [x] Unified config system
• [x] Move config logic into module package
• [x] Build synapse binary which can run any of the necessary packages

[meyer9]

The last part of this is to implement a common interface for modules which should basically just be:

type Module interface {
    Run() error
}

Then, we should build out the synapse module which will take in just global options and run apps based on the configs provided.

[codecov-io]

Codecov Report

Merging #102 into master will increase coverage by 0.99%. The diff coverage is 26.31%.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
+ Coverage   48.13%   49.13%   +0.99%     
==========================================
  Files          42       43       +1     
  Lines        4531     4441      -90     
==========================================
+ Hits         2181     2182       +1     
+ Misses       2070     1981      -89     
+ Partials      280      278       -2

Impacted Files	Coverage Δ
shard/transfer/transfer_shard_code.go	16.66% <ø> (ø)	:arrow_up:
beacon/syncmanager.go	0% <ø> (ø)	:arrow_up:
primitives/state.go	55.07% <ø> (-0.07%)	:arrow_down:
utils/net.go	0% <0%> (ø)
primitives/validator.go	88.46% <71.42%> (+6.98%)	:arrow_up:
beacon/db/badger.go	0% <0%> (ø)	:arrow_up:

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