[MUS-95] add code quality checker

- add sample ui test case with robotium
- add support for Android Studio 8.1

"gradle check test connectedAndroidTest" works
missing:
- new Jenkins Jobs with Gradle has some problems [1]
- automatic nightly build Job

[1] https://jenkins.catrob.at/view/All-Categories/view/Musicdroid/job/Musicdroid-Custom-Branch-Gradle/