User-facing changes:
* Don't backup on metered networks
* Disable spell-checker on recovery code input
* Disable Nextcloud restore when not installed and no store available
* Ask for system authentication before storing a new recovery code
* Prevent screenshots of recovery code
* Add expert settings with an option for unlimited quota
* Allow launching restore through a dialer code
* Restrict exported components
Others:
* Improve .editorconfig setup
* Move LocalContactsBackup to product partition
* Link FAQ in Readme to make it more discoverable
* Compares kotlin-bip39 library with bitcoinj library
* Provide an overview over key derivations
* document potential information leakage through the long-lived SQL caches
* Add warning for third-party tools to README
Change-Id: I095af13d0ff010c9602bc323267c074ce7d019a2
