added mapbox provider dpmap implementation.
code cleanup.
increase features of the map interface.
cleaned up dp map interface.
Remove TAKEOFF from mission item fragment type list if there is more than 1 item in mission list
Allow LAND and RTL mission items to be set only in the end of mission list
Fix TAKEOFF item handling
Stop new mission items addition after RTL or LAND
Merge pull request #959 from alextel69/fix-takeoff-land-sequence

Fix TAKEOFF-LAND (RTL)  sequence

Closes #794
Merge branch 'master' of https://github.com/DroidPlanner/droidplanner into feature_mapbox_integration

Conflicts:
	Android/src/org/droidplanner/android/fragments/DroneMap.java
	Android/src/org/droidplanner/android/fragments/FlightMapFragment.java
	Android/src/org/droidplanner/android/fragments/SettingsFragment.java
	Android/src/org/droidplanner/android/maps/DPMap.java
	Android/src/org/droidplanner/android/maps/providers/DPMapProvider.java
	Android/src/org/droidplanner/android/maps/providers/google_map/GoogleMapFragment.java
	Android/src/org/droidplanner/android/maps/providers/osm/OSMapFragment.java
	Android/src/org/droidplanner/android/utils/DroidplannerPrefs.java
	Android/src/org/droidplanner/android/utils/DroneHelper.java
Merge pull request #960 from arthurbenemann/libraries-move

Moved External libraries to Libraries folder
preferences update
updated DPMap api.
updated DPMap implementations to match above update.
Merge branch 'master' of https://github.com/DroidPlanner/droidplanner into feature_mapbox_integration
Mapbox 'goToMyLocation', 'goToDroneLocation' bug fixes.
Make Circle Item work again on AC 3.2RC3 or higher
Move Circle fragment to the right location
Fix paths broken by last commit
Merge pull request #970 from arthurbenemann/circle_fix

Circle Item fix
Version: Releasing version 2.6.1