user-accounts: Make malcontent-control optional
Hide the button to open the parental controls UI if it’s not installed. This will allow distributions to split the dependency, making gnome-control-center suggest (rather than require) malcontent-ui, while still requiring libmalcontent.
In turn, this will allow malcontent-ui to be uninstalled without requiring gnome-control-center to be uninstalled, which will satisfy users who feel the need to uninstall it because it’s not useful to them.
Signed-off-by: Philip Withnall pwithnall@endlessos.org