[WIP] 3pv follow ui

Here's a new interface for ~~Follow Me~~ 3PV.  The screen was getting too cramped with the old style, so it's a new activity now.  The cramped screen was really only a problem on phones, but honestly, you shouldn't be doing 3PV with a tablet (unless you're one of those people that takes pictures with an ipad).

There are two "control" buttons.  The first is a takeoff/RTL button (depending on is_flying).  The second one is loiter/follow (only allows you to start follow if you're in loiter).

TODO:
- [ ] Make sure nothing is broken on tablets.  Someone else needs to test it because I don't have one.
- [ ] String extraction and Localization
- [ ] Make control buttons actually work
- [ ] implement Status checks
- [ ] increase brightness of icon.  (try the other icon in /res/ before making a new one)
- [ ] make interface nicer
- [ ] Allow changing of altitudes when not in guided mode

![screenshot_2014-09-07-19-47-54](https://cloud.githubusercontent.com/assets/2956460/4180159/69663af8-36ea-11e4-99f0-7f976f0f6c37.png)

![screenshot_2014-09-07-19-59-41](https://cloud.githubusercontent.com/assets/2956460/4180170/1c325838-36eb-11e4-88c2-1818a1b4287b.png)