Animate change month, add onDateLongClick

I've added a onLongClickDateListener so the longClickEvent can also be used
There's also a custom setAnimatedScroller to animate the change date (if you swipe to less it will animate back too)
The last change are new drawables to clean up the CaldroidView (especially a onClick-graphic for the next/back buttons on top)

Sorry this is my first pull-request. I tried to make it as simple as possible.