Added the ability for an element to paint on itself after its children have been painted.
#27: Fixed the cursor rendering.
Unfortunately, I had to make a full render of the text field every animation frame instead of using just the rectangle around the cursor, which I should be able to do.  That was causing the weird rendering problems I was seeing before.  Have to fix this next.
Changed the base texture to clip to the given bounds.  This fixed some rendering issues.
Fixed another rendering bug
#27: Re-added the code that makes the cursor blink render only on its rectangle instead of the entire text widget