Added HUD improvments from AndroPilot
New way to select where to add a polygon point, now the UI behaves better.

I have made some changes to the polygon point insertion algorithm on polygon mode, it works really well (polygons points are added based on the distance, not on a simple sequence).
Adds the posibility of using offline maps on the GCP activity.
Fix bug when updating an offline Map.

When using offline maps the overlay must be added every time the map is cleared.
Adds a preference for using offline maps in the GCP screen.

Also refactor some functions to a new helper class.
Refactoring the package structure.