lockscreen: Disable authentication with 'disable-pin' setting
Adds a boolean key disable-pin
to sm.puri.phosh.lockscreen
settings schema and uses it to determine whether entering the PIN (or password) in the lockscreen is required. In other words, setting this key to true
disables authentication in the lockscreen.
Not tested with every possible lockscreen feature (calls, plugins etc.), but works at least in simple use.
Fixes #558.