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? 
Nice. Drawing our own line is better than adding more views to the hierarchy to handle this. I think I saw Lucas doing something similar in a bug recently, you could ask him for advice here as well.