Match EntityId changes in DataModel.

This commit makes Wikibase use the EntityId rewrite in DataModel
done in https://gerrit.wikimedia.org/r/#/c/80394/

This commit mainly includes:

* new EntityId to new ItemId or new PropertyId
* updating references from Wikibase\EntityId to the new location of EntityId
* constructing EntityIdValue instead of EntityId where applicable
* removal of id parsing and formatting no longer needed
* addition of code required to ensure compatibility
* random cleanup of code already touched by this commit

Change-Id: I8fba1e700fe435c96618c2ab75e3bebe5363561e