Qml pfd markers

This adds support for visualizing the home location and waypoints relative to the vehicle.

In addition, several math bugs were also fixed. They went unnoticed till now because they were minor, or in the case of the compass module unused.

This shows the magenta waypoint. (The home location looks identical, except it's yellow)
![Screen Shot 2013-04-21 at 12 09 01 AM](https://f.cloud.github.com/assets/1118185/405757/f4a7f614-aa06-11e2-9310-92b5a64ea570.png)