A bug caused by not passing the index argument to `ControllerActivity` led to all preferences opening the activity that pertained to Controller #1. This was fixed by passing the `index` argument in the activity launch intent.
* Update licenses for dependent projects
* Add copyright notices (as provided)
* Revamp styling for `LicenseDialog`
* Fix invisible `PreferenceDialog` buttons in Settings
* Consolidating color variables into `colorPrimary`, `backgroundColor` and `backgroundColorVariant`
* Use `com.google.android.flexbox:flexbox:3.0.0` (Google Maven) rather than `com.google.android:flexbox:2.0.1` (Bintray)