Add configurable filter search box to terms panel

This pull requests adds a search box on top of the terms panel. The search box can be enabled and disabled in the panel editor. The search box has a (configurable) search history as well.
This box will add a prefix query to the panel query on the field on which the panel is running the facet.

There is one minor bug which I haven't been able to solve: when you change options in the panel editors (e.g. increase/decrease the number of queries kept in history), the ng-submit action is not called anymore for no obvious reason.