Events taxonomic coverage indexing

[fmendezh]

The taxonomic coverage of an event can be interpreted as the aggregation of taxonomic coverage of sub-events and associated occurrence records.

Aggregating taxonomic data can facilitate the discovery and exploration of events based on ranks and specific taxon keys.

Particular cases that must be taken into consideration:

• An event contains a large number of classifications derived from sub-events and occurrences
• An event can contain a classification, interpreted from its identification terms, different to one derived from sub events and occurrences.

[djtfmartin]

This worked is done and has been merged in the develop branch.