[Android] Deep Links, Push Notifications, & Other Infrastructure Setup

[moiz994]

Implementation of the required infrastructure to easily implement Deep Links and Push notifications with third-party tools.

### Tasks
- [ ] https://github.com/openedx/openedx-app-android/issues/202
- [ ] https://github.com/openedx/openedx-app-android/issues/203
- [ ] https://github.com/openedx/openedx-app-android/issues/204
- [ ] https://github.com/openedx/openedx-app-android/issues/218

[marcotuts]

Anything here that should move to the Q3 cleanup / bugs effort? I'm assuming this is ready to mark done, but for now I've just moved to In Acceptance. fyi @moiz994