Transport selection

Replace ContextMenu with popup to temporarily change preferred transport on longpress of send button.

![screenshot](https://cloud.githubusercontent.com/assets/373823/3654788/8b2549d0-1170-11e4-8ea2-70ec26f0abe9.png)

Is it possible to pull out everything here which loads and keeps track of the strings and images and resources into a class which is responsible for managing them, and then simply returns a TransportOption which will give you the sendButton image drawable, compose text hint, in addition to whether it's forceSms or forcePlaintext, etc?