LockSettingsService: move database storage

The database storage commands are part of ILockSettings, but the actual
storage takes place on LockSettingsStorage. Redirect the calls in
LockSettingsService to LockSettingsStorage to make the ownership a bit
more clear.

Test: atest LockSettingsStorageTests LockSettingsServiceTests
Change-Id: Ibc9236a171cedd3b09b1afed70895bc91e895a1c