Add dockerfile and minor improvements to listener

[alejgh]

Closes #44

Additionally, the following functionality was added:

• Use a production-ready server when the FLASK_CONFIG environment variable is set to production.
• Use OAuth to download the diff files from the Github API.
• Perform the synchronisation in a subprocess instead of sequentially when responding to a request.

[alejgh]

Alright, where to start...

There was a problem when deploying the application using Docker where the container was able to connect to any place except to the Wikibase instance where the synchronisation needs to take place (this instance was launched on the same host machine).

I'm not going to go into details but it is a problem related to the firewall and Docker. The following solution worked for me: https://stackoverflow.com/questions/43879637/docker-container-cannot-connect-to-host-machine-no-route-to-host

[alejgh]

I will add two additional commits now and see if the coverage is ok.

Functionality-wise everything is ready.

[codecov[bot]]

Codecov Report

Merging #45 into master will decrease coverage by 0.11%. The diff coverage is 95.00%.

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
- Coverage   97.61%   97.50%   -0.10%     
==========================================
  Files          15       15              
  Lines         668      680      +12     
==========================================
+ Hits          652      663      +11     
- Misses         16       17       +1     

Impacted Files	Coverage Δ
...ules_sync/synchronization/ontology_synchronizer.py	95.46% <ø> (ø)
hercules_sync/listener.py	90.70% <94.12%> (+0.08%)	:arrow_up:
hercules_sync/git.py	96.97% <100.00%> (+0.04%)	:arrow_up:

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