The new manifest yields much better flatpaks for our end-users:
- Fewer permissions are requested
- Fixed app icon
- Release build instead of a debug build
With this change an unlock stage is introduced to loading account storage.
Key derivation parameters for a master key are recorded, and the master
password may be supplied to "unlock" the account secret(s) in storage.
This change paves the way for actually decrypting encrypted account
secrets later, and finally solving issue #6.