Gradle files for Android Studio 0.5.1+ (Gradle 0.9+)

As discussed in #3636, I created Gradle files for c:geo to use AndroidStudio.
It includes unit tests and debug/run buildtype for use with AndroidStudio (especially).
There are only additions.
Works for Android Studio 0.5.1+ / Gradle 0.9+

Before usage, you still need to copy keys.xml.

For unit/instrumentation tests, (gradle task 'connectedAndroidTest'), you need to replace custom namespace with xmlns:cgeo="http://schemas.android.com/apk/res-auto"
I don't know if a such change is backward-compliant, so i don't put it in this pull request.