gradle plugin update.
unused string cleanup.
removed mapbox map implementation.
removed use of android api within a core class.
removed unused attributes, and resource files.
removed unused menu resources.
updated travis configuration file.
Merge pull request #1279 from ne0fhyk/code_cleanup

Code cleanup
Merge branches 'dp_3dr_services' and 'master' of https://github.com/DroidPlanner/droidplanner into dp_3dr_services

Conflicts:
	Android/res/values/attrs.xml
	Android/src/org/droidplanner/android/activities/helpers/SuperUI.java
	Android/src/org/droidplanner/android/maps/providers/mapbox/MapBoxFragment.java
	Android/src/org/droidplanner/android/utils/DroneHelper.java
	Core/src/org/droidplanner/core/MAVLink/MavLinkMsgHandler.java
Merge branch 'master' of github.com:3drobotics/3DRServicesClient into dp_3dr_services
code cleanup.
Merge branch 'dp_3dr_services' of https://github.com/DroidPlanner/droidplanner into dp3

Conflicts:
	Android/src/org/droidplanner/android/maps/providers/mapbox/MapBoxFragment.java
	Android/src/org/droidplanner/android/maps/providers/mapbox/MapBoxProviderPreferences.java
	gradle/wrapper/gradle-wrapper.properties