Allow multiple select in autocomplete

This patch will update of both display and hidden related element field.
Values are separated with comma.
Rename variable since $ sign typically denotes a jquery object
Prevent XHR request when query length does not satisfy minLength
Merge branch 'pr/553' into 2.2

* pr/553:
  Prevent XHR request when query length does not satisfy minLength
  Rename variable since $ sign typically denotes a jquery object
  Allow multiple select in autocomplete

Closes #553