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.
more testing.
updated the set of files to be uploaded in releases for deployment.
Merge branch 'feature_travis_ci' of https://github.com/DroidPlanner/droidplanner into feature_travis_ci

Conflicts:
	.travis.yml
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
Merge pull request #822 from ne0fhyk/feature_travis_ci

Feature travis ci
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.
fixes travis ci failures because of licenses.
Merge pull request #824 from DroidPlanner/feature_travis_ci

Fix travis ci failures
Merge branch 'master' of https://github.com/DroidPlanner/droidplanner into feature_analytics
updated gradle tools version to support android studio beta release.