Font, text color, and background color customizations; alternative setter for header title color; fixed bug causing today's date background color to show in adjacent month hidden cell

Implemented the following customizations while keeping existing defaults:

* Added font customizations for header, weekday, day, and today labels.
* Added text and background color customizations for enabled and disabled day label.
* Added alternative setter for existing header title color that optionally reloads data (existing setter always calls reloadData).

Bug fix:

* Fixed bug causing today's date background color to show in corresponding hidden cell in adjacent month (e.g. Jan 2, 2014 cell in December 2013 or Dec 30, 2013 in January 2014).