Bug 1042960 - Create UI elements for facet bar

This is a WIP that addresses two challenges with the design for bug 1042960.

1) One-sided borders are tough. They require hacky layer lists or a 9 patch, which is doable, except:
2) How would we change their colors based on the search engine? 
When will we want to dynamically change the color of the underline? If we create these buttons from search engine information (we'll need to know the name/endpoint for the facet), then we should have the color when they're created. I think it would be fine to require that the color is just something that is set once when the view is created.