less error prone jQuery.wikibase.siteselector matching character highlighting

* site selector will no longer fail in case the input matches some site while the string
  representing the site as list item within the selector does not contain that string
* use language code instead of site ID for the site name + language code labels
* minor test improvements

Change-Id: I6ca7e4795b127aea1072e33db5fc8a34e144702f
Merge "less error prone jQuery.wikibase.siteselector matching character highlighting"