Android adapter

[mwcampbell]

I will start working on the Android platform adapter soon. I plan to do this in two stages: first, supporting basic widgets other than text, and second, implementing text support.

[DataTriny]

I have pushed a branch named android-basics-old on this repo. It contain what I did when I started working on this a long ago. Feel free to reuse pieces of it, there might be something valuable.

[DataTriny]

Implemented in #500.