APIv4 - Refactor Entity.get and deprecate the includeCustom param

This makes Entity.get more efficient - it no longer does a file scan when getting one or more entities by name.
Also deprecates the includeCustom param which was redundant with the where clause.
This is the first APIv4 param to be deprecated - added handling to emit a warning when using a deprecated param
and hide deprecated params in the APIv4 explorer.