(bug 45002) additional experts for jQuery.valueview

* Introduction of a "BifidExpert" which is an abstract valueview expert definition which requires
  two other expert constructors in an implementation. The bifid expert will choose one of the two
  other experts depending on the valueview's current mode. This allows greater flexibility when
  defining new experts and allows for sharing code more efficiently.
* SuggestedStringValue expert which is basically a StringValue expert plus suggester jQuery
  widget on top. Also see the TODOs in the documentation.
* Introduces a "StaticDom" expert which can be used together with the "BifidExpert".
* Reintroduction of special handling for string data values that should match the CommonsMedia
  data type definition. This is done with a CommonsMediaType expert. This expert is combining the
  three experts described above.
* Added the commons media support to MediaWiki's default expert factory.

Change-Id: Ibf778f2ab544ec51f8f9574eb32aea82a5707caf