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