SDLSurfaceView: add `OnKeyPreIme`  listener closes github/kivy/kivy#1066
initial attempt at swiping support
swype input: simplify IME management, allow text predictionto work
and ensure IME doesn't take up entire screen in landscape mode

Tested with::
- Stock JellyBean keyboard with swiping and text prediction
- SwiftKey with flow and text prediction
- Swype Keyboard with swiping and text prediction
SDLSurfaceView: add suport for forwarding keystrokes while text
prediction is working not just at the end.
Merge pull request #104 from kivy/1066

Swype Input Support