Blend premultiplied alpha PNGs correctly on Apple plaforms.
Remove reference to pygame causing ImportError.

In particular, iOS platforms don't ship with pygame.
Ensure premultiplied colour is applied to entity on Apple platforms.
Fix text blending on some (non Apple) platforms.

Rather than just change the blend mode, introduce
separate methods of rendering text depending on platform.
Clean up underlying image in Text entities. Refactor label usage in text image generation.
Temporary fix to improve quality of text on Apple devices.

Remove colour from text and replace with gray with current alpha.
added fix to colour requesting methods so premultiplied alpha is applied on osx and ios
Merge pull request #24 from arcticshores/kivy-backend

Various changes mostly related to iOS alpha issues