Expliclty use FilteredSelectMultiple for WebHook form's repo field

Review Request #8225 — Created June 8, 2016 and submitted — Latest diff uploaded

Information

Review Board
release-2.5.x
ea2e0bc...

Reviewers

The repositories field of the WebHookTargetForm now explicitly uses a
FilteredSelectMultiple widget. While WebHookAdmin specifies that
this field in filter_horizontal, if any non-admin page should use this
form they will want to use a FilteredSelectMultiple for this widget.

Tested this with an upcoming patch in RBCommons.