Refactor synchronization logic.

[alejgh]

We have moved most of the synchronisation logic from this repository to wikibase-sync. From now on, this repository will consist of the particular aspects of synchronization of GitHub repositories to a Wikibase instance. This includes:

• Handling of requests from WebHooks.
• Using the GitHub API to compute the diff between two releases.
• Creation of a web service that can be launched with Docker to execute this automatic synchronization.

All of the code regarding the synchronization logic given two RDF strings to a Wikibase is now handled in wikibase-sync.

The only mature change that was needed for this refactor was the modification of the OntologySynchronizer class to handle the source and target contents to be synchronised separately instead of receiving an instance of the GitFile class. To sum up, we decoupled the synchronization logic from the use of Git for this refactor, and now any string from any source can be given instead.

It is expected to have a decrease of code coverage as a consequence of this change, since most of the test cases were targeted at the business logic of the synchronization itself and not at the web service. Due to that, I think it is fair to make an exception in this pull request regarding a decrease of code coverage. However, coverage should still remain at least greater than 90%.

[codecov[bot]]

Codecov Report

Merging #71 into master will decrease coverage by 2.34%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #71      +/-   ##
==========================================
- Coverage   98.30%   95.96%   -2.33%     
==========================================
  Files          15        3      -12     
  Lines         762      198     -564     
==========================================
- Hits          749      190     -559     
+ Misses         13        8       -5     

Impacted Files	Coverage Δ
hercules_sync/listener.py	91.49% <100.00%> (ø)

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