Updating the Zenodo handling

[davidorme]

This PR expands a bit of the actual issue described in #161 after feedback from Sam.

• Sam's error came from using outdated/incorrect URLs for the Zenodo API endpoints. I've done two things:
  • Removed the Zenodo API endpoints from the configuration file and hard-coded them. Seemed oddly fussy and not something that changes (often!) and this avoids a simple configuration issue.
  • Updated the Zenodo error handling to report some more basic information and then adding additional JSON data only if available (not all zenodo responses provide additional JSON info),
• I've added mutually exclusive --live and --sandbox switches to the Zenodo commands to allow data managers to switch the target publication site without having to maintain different config files.
• I've update the "Using safedata" section for Data Managers to include separate sections on validation, publication and posting metadata, with more discussion of the key points and more example outputs.
• Updated the code to handle the change in the new version generation on Zenodo - this has shifted from creating an empty deposit from the concept ID to creating a clone from the most recent record ID. The publish_dataset function now does some filename and hash checking to work out how to align the files being provided with what is already online. Docs updated to reflect this.

Closes #161

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 13.60544% with 127 lines in your changes missing coverage. Please review.

Project coverage is 77.88%. Comparing base (9324649) to head (9e56bf1). Report is 20 commits behind head on develop.

Files	Patch %	Lines
safedata_validator/zenodo.py	5.51%	120 Missing :warning:
safedata_validator/entry_points.py	65.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #162 +/- ## =========================================== - Coverage 79.04% 77.88% -1.17% =========================================== Files 13 13 Lines 3741 3807 +66 =========================================== + Hits 2957 2965 +8 - Misses 784 842 +58 ```

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[davidorme]

@jacobcook1995 I haven't tested this stuff, but it does it look sensible? Still need to figure out what went wrong with Sam.

[davidorme]

@jacobcook1995 This is changed again with the update to match the changed Zenodo new version process. I think this is a sensible resolution (use md5 and filename to check for new/changed/unchanged/removed files) and I've updated the docs to match.