Add a list of allowed badges to Special:SetSitelink

The textfield for badges has been replaced by a multiselect box which
lists all badges available. Currently the serialized item ids of the
badges are displayed but have to be replaced by their labels if available
in another patch when we have found a nice way to query them.

Bug: 61664
Change-Id: I22d1e746a8e5df55988b6e12ea00619989406742
Merge "Add a list of allowed badges to Special:SetSitelink"