Possible improvements in performance

[alejgh]

There is currently a bottleneck with the execution of operations to the triple store (addition, removal...). These are some possible performance improvements that could be done:

• Add a new BatchOperation that executes at once all the operations of a given subject (create it if needed and write all its related statements at once). We also need to provide a way to transform multiple simple operations into BatchOperations.
• Use the fast run mode from WikidataIntegrator.