There are a bunch of settings which are synced an not handled by
desktop, one of them being the `profile-pictures-show-to` setting.
This commit introduces a new `SettingsFieldDto` so we can react to
message signals that include individual setting fields that originate
from syncing.
The first setting hanlded is the one mentioned above, so a new
application signal is introduced to inform the app that there was an
update in that particular setting, so it can re-render the view.
Partially addresses #5201
882c0dcc2b