Use in LabelLookup (w/ EntityRetrievingTermLookup) in EntityIdLabelFormatter

this moves the label lookup code out of the formatter,
and into the EntityRetrievingTermLookup and then injects
a LabelLookup (albeit still using EntityLookup) into
the EntityIdLabelFormatter.

in comparing the TermIndex (database) TermLookup vs this,
it seems this is better option (loading the entire entity from
memcached) of the two when doing many lookups.

and makes it easier to swap in a batching lookup or other
implementation at a later time, depending on the use case.

Change-Id: Ia6a968d289cefc2e4df917b60dc761652d8354b6
Merge "Use in LabelLookup (w/ EntityRetrievingTermLookup) in EntityIdLabelFormatter"