Following up on discussions taken place at https://github.com/aerogear/aerogear-android-sdk/pull/74

Tasks:

• Clean up the current code base by simply running the IDE (Android Studio) reformat tool. This won't do any refactorization or change in code, it will only do some ornamental changes (spaces, indentation..) and remove unused imports.
• Enable linter checks during build time so that it fails if code doesn't follow our formatting standards (Android Studio / IntelliJ defaults). This should affect both building locally and by CI.