register as an SMS provider for 4.4 kitkat

I saw there was another PR for this opened, but the owner had no movement in the last week so I thought I would open this in the interest of time. This does the bare minimum to get text secure working properly in KitKat. It does not implement any quick response functionality, to keep it simple. 

I corrected a lot of messy whitespace in the manifest; I can revert if you don't want that.

I've tested and it works as expected in both KitKat older android. As a nice to have, it would be cool  for the app to display a banner when it is notnot the default SMS app, similar to stock SMS app.