Spline Path integration and Maps refactoring

@arthurbenemann, the spline path integration leverages the work done in the map refactoring. As such, I'm reusing the same branch.

This pull request adds support for mission planning via spline waypoints / spline path.
The integration was successfully tested against a quadcopter with a pixhawk autopilot running AC3.2.

Here are some media showcasing the updates to Droidplanner to support the feature:

### Testing 1:
* Mission setup: http://youtu.be/bm_q2fCi2uA
* Mission flight: http://youtu.be/-_Fjh5q8b1M

### Testing 2:
* Mission setup: http://youtu.be/t8wExKZC2Zc
* Mission flight: http://youtu.be/zgD_6uyVSgg