Accessibility update; ViewGroup positioning; DownUnder mode for default in & out animations.

- The Accessibility feature wasn't working in JB, added a fix for JB ontop of the legacy method.
- Added means to specify positions (start, middle, end) to place Crouton in a ViewGroup.
- Updated DefaultAnimationsBuilder to provide an in animation that slides up and out animation that slides which is used when the Crouton is at the end^ position of ViewGroup OR DownUnderMode flag is set for in or out animations.

 ^ that might not be desirable for all cases, perhaps DownUnder mode should only be applied if DownUnderMode flag is specifically set for animations?

Also note: I haven't tested the new features with multi-line Croutons.