Subscriptions in database: UI (#111)

* Removed permissions requesting

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Migrated loading to database

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Minor changes

* `add` returns ids

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Migrated creation to database

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added update method

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Changed ViewModel

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Removed active switch

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Migrated edit to database

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Rework EditCalendarActivity

- use explicit EXTRA_SUBSCRIPTION_ID
- use ViewModelProvider.Factory instead of custom loadSubscription()
- create one-two-one relationship between Subscription and Credential

* Added permission extra

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Moved permission request

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added permission required Snackbar

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Fixed permission request

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added `showCalendarPermissionNotification`

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added notification permission requests

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Added calendar permission notification

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Changed threading (#112)

Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>

* Change model/view/result pattern to states (LiveData)

* Don't ask to enable sync framework auto-sync because we don't use the sync framework anymore

* Remove unneeded string

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Signed-off-by: Arnau Mora <arnyminer.z@gmail.com>
Co-authored-by: Ricki Hirner <hirner@bitfire.at>