Fix endDate trigger; add config options for period labels; trigger change for month-select, year-select, decade-select.

[jlong4096]

Three updates we found useful while integrating this project into our application.

1. Selecting a new endDate will now trigger the callback.
2. Day/Month/Year etc labels are now configurable.
3. When the select value for the month, year, decade select fields change, onChange is now fired (this allows for jQuery to hook into when these fields are changing).

I've never used coffee-script or knockout before, so I apologize in advance if there are any glaring issues with my changes.

[krnlde]

What a pitty. This lib is so cool, but doesn't get this truly nice PR merged :(