Gradle update and optimisation

Updated Gradle to 1.12 and the Android gradle plugin to 0.10. Now
Atarashii can be built again without troubles (with the latest Android
Studio 0.5.8). Also done some optimisations to the gradle config:
- defined things required for all modules in the root build.gradle
- kept the wrapper tasks in the build.gradle files for easier update
  in the future
Merge pull request #165 from d-sko/gradle_update

Gradle update and optimisation (also fixes Android Studio building)