[sddm-theme] Handle passwordless accounts
As described here https://github.com/sddm/sddm/issues/751#issuecomment-847347450
SDDM provides the needsPassword
property, which can be used to hide the password prompt for passwordless accounts.
This merge request provides a basic implementation for the breeze SDDM theme.
The addition was tested at tag v5.18.4.1 on Ubuntu 20.04.2 LTS (Focal Fossa).
It has been merged into work/tpecar/sddm-theme-passwordless
which has been based on current master (2f4b27fc).