cosmic-settings-daemon: make geoclue optional

[fsvm88]

Hey @joostruis , I had to re-add geoclue as a hard requirement due to pop-os/cosmic-settings-daemon#14

It seems like everything is working, but without geoclue cosmic-settings-daemon will always exit with rc 1 any time it is invoked (visible in journal logs).

I'm opening this issue to keep track of the original one, so that we can make it optional as soon as that one is resolved.