Add batch operations

[alejgh]

Closes #41.

We have added a new way to perform operations more efficiently with Wikibase. The following features were added:

• New function to optimise basic operations into batch operations.
  • Batch operations are considerably more efficient when there are many updates to execute for the same set of subjects.
  • All of these operations are executed in a single transaction, minimising the performance overhead of communicating with Wikibase.
• Small refactor of the WikibaseAdapter class to minimise the calls to the wdi_core.WDItemEngine write method. We are making as many calls as possible to the update method instead, in order to reduce the writing operations to Wikibase and improve the overall performance.

This will unlock the start of #60, where we can illustrate with a visual approach the improvements that have been made.

[codecov[bot]]

Codecov Report

Merging #61 into develop will decrease coverage by 0.06%. The diff coverage is 99.11%.

@@             Coverage Diff             @@
##           develop      #61      +/-   ##
===========================================
- Coverage    98.08%   98.03%   -0.05%     
===========================================
  Files           15       15              
  Lines          728      760      +32     
===========================================
+ Hits           714      745      +31     
- Misses          14       15       +1     

Impacted Files	Coverage Δ
hercules_sync/synchronization/algorithms.py	100.00% <ø> (ø)
hercules_sync/synchronization/operations.py	98.08% <96.78%> (-1.92%)	:arrow_down:
hercules_sync/synchronization/__init__.py	100.00% <100.00%> (ø)
hercules_sync/triplestore/triple_info.py	99.39% <100.00%> (+0.02%)	:arrow_up:
hercules_sync/triplestore/wikibase_adapter.py	100.00% <100.00%> (ø)

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