• Bug fixes and performance improvements

## Added
- Message pinning
- Scheduled messages
- One time QR code login

## Changed
- Design improvements

## Fixed
- another app instance is opened after opening media files or shared files screen
- various bugs (also thanks to @p1gp1g )

Minimum: NC 17 Server, Android 8.0 Oreo

For a full list, please see https://github.com/nextcloud/talk-android/milestone/106?closed=1