Introduction of valueview expert for time value handling

* TimeInput expert responsible for handling the input of time. This will require some refactoring
  when adding advanced handling. Right now this is inheriting from StringValue which is kind of
  abuse of inheritance but allows a simple first implementation of editing and displaying time
  values.
* TimeValue expert which is a BifidExpert using the TimeInput expert and the StaticDomExpert.
* introduces a minor fix for the BifidExpert's valueCompare function.

For usage with Wikibase, this also requires I1f6dc90.

Change-Id: I6af96084c643ffb67fd3aa99bc9e039ccdfc55e1