(bug 44713) entityselector: Option to define custom aliases label

The change set allows passing a custom label to the entity selector widget for the list of
aliases shown when there is a search hit on at least one alias of an entity.

Change-Id: Idf4e734d4b2ec2ba6da1338571c6edcab071be2c
(bug 44713) entityselector: Using messaging system if available

Entity selector widget will try to retrieve its messages via the mediawiki messaging system
if available.

Change-Id: I6400c8131d2bcfcb32e09947f2792beb5ee88597
Merge changes I6400c813,Idf4e734d

* changes:
  (bug 44713) entityselector: Using messaging system if available
  (bug 44713) entityselector: Option to define custom aliases label