CleanUp: Removing Old Translations
CleanUp: Removing unused strings as reported by android lint tool.
CleanUp: Extracting strings from the arrays file
CleanUp: Regrouping strings into logical groups
Updated submodules
Basic Gradle and .iml files. Adjusted .gitignore
Fixed missing value, fixed duplicate entries
Adjusted SDK version in AndroidManifest, fixed a duplicate entry
"Redirecting" all Android Support library dependencies to sub project
Updated README
Merge pull request #619 from zumbrunnen/gradle

Gradle support
Updated submodules to most recent commits
Updated project.properties to use API 19
Removing *.iml from version control

They contain too much local info and change arbitrarily
Dependency cleanup

 * Android Support as a Maven dependency
 * Removed UsbSerialLibrary include from settings.gradle
 * Removed Play Services dependency for Mavlink
Ignoring sub project 'google-play-services_lib'

... and adding the dependencies directly in the main project
Support library and Gradle version upgraded
Updated submodule refs
Merge pull request #623 from zumbrunnen/gradle_cleanup

Gradle Cleanup
added check for the google play services version. Should help with issues like #631