Backup user presets to the cloud

[mikimn]

As a user, I want to be able to back up my presets to the cloud, so that I can easily migrate and manage them across devices.
This has a few benefits:

• A user migrating to a different hand can also migrate his preset information (which is currently stored on the hand's hardware)
• A user migrating to a new Android device gets to keep all preset names.

So, this issue has 4 core components:

1. Introduce Firebase Authentication and Firebase Cloud Firestore support to the app
2. Allow a user to log into the app using some authentication method (email/password, Google, Facebook)
3. Backup the user presets and load them from the cloud when possible

In the future, we might also add a "Migrate" option so that the user can migrate presets from and old hand to a new hand, by updating the BLE identifier across the database documents.