Swype Input Support

closes http://github.com/kivy/kivy/issues/617
Swype Input Support, allow text predictions to work and
ensure IME doesn't take up entire screen in landscape mode.

Tested with ::
- Swype Keyboard. Swiping and text prediction works
- Swift Key Keyboard Swiping and text prediction both works.
- Jellybean stock keyboard. Swiping and text prediction works.

closes http://github.com/kivy/kivy/issues/1066
Pressing the back button when Android on screen keyboard was open lead to Ime eating up the event. implementing a `OnKeyPreIme` event allows to catch the `back` button before it's passed on to the keyboard.