integration of google analytics within droidplanner.
fixed issues preventing google analytics from dispatching recorded hits.
cleaned up the styles resource file.
added preference to disable usage statistics reporting.
added 'up' navigation button to the settings screen.
Added 'mode details panel' usage tracking.
created package for analytics related code/logic.
added a Category enum to store all analytics related categories.
Merge branch 'master' of https://github.com/DroidPlanner/droidplanner into feature_analytics

Conflicts:
	Android/res/xml/preferences.xml
Merge branch 'master' of https://github.com/DroidPlanner/droidplanner into feature_analytics

Conflicts:
	Android/res/xml/preferences.xml
added ga tracking for the flight action buttons usage.
added documentation stub for the drone event types.
bug fix.
added tracking for mavlink connection methods.
fixed license issue with travis ci.
second attempt at fixing travis ci license issue.
updated connection type session on disconnection.
fix gradle tools version.
Merge branch 'master' of https://github.com/DroidPlanner/droidplanner into feature_analytics
updated gradle tools version to support android studio beta release.
updated the android plugin declaration style.
completed analytics feature list.
Merge branch 'master' of https://github.com/DroidPlanner/droidplanner into feature_analytics
specifying required libraries for the travis ci build.
attempt to fix travis ci build issues by using deprecated google analytics hit builder.
Merge pull request #829 from DroidPlanner/feature_analytics

Google Analytics update