style(datepicker): redesigned for bootstrap 3

This redesigns the datepicker to conform to new Bootstrap 3.

As a side note, this is a complete redesign from the original styling of the datepicker. 

- It is now a fixed-width control (240px without weeks, 280px with). This is a fairly natural way to design tabular data where each cell needs to be exactly equal in width. 
- The popup no longer has the buttons at the base of the control. I removed them since this appears to be the primary use case (just a plain ol' calendar... ala http://eternicode.github.io/bootstrap-datepicker/). Since that is handled entirely through templates it's fairly easy to fix if certain controls are needed in the popover. 

That's about it, if anyone dislikes how the new control looks let me know and I can play with it.