Keepassxc: Default expiration setting

[rugk]

Add a default expiration setting for new password entries.

Expected Behavior

Add a setting to enable a default "expire time", e.g. "two weeks" or "3 months" relative to the creation of the password entry, that is set by default when you create a new password.

Current Behavior

Ýou always need to specify such an expiration manually.

Context

Inspired by https://github.com/keepassxreboot/keepassxc/issues/551#issuecomment-445272773, who seems to not wanted to create a new issue for that suggestion.

[droidmonkey]

This should be a per-group setting similar to default auto-type for a group.