add option to disable photo scan

I had a look a the Maps app, thought "looks interesting, I'll explore this later today". Jumped on the tractor to get a snow blade, came back and noticed the News app had stopped updating (again). OK, so I need to clear out a stuck job from the oc_jobs table again, here goes...

...only to find out it wasn't News which got stuck - it was fine - but Maps which was busily adding photo scan jobs. Lots of jobs... I disabled the app and killed the active scan jobs, removed about 400K entries from oc_jobs and all was fine again.

While I understand that those who enable GPS tagging on their cameras and phones like to use this feature to locate their photos on a map it should be clear that those of us who always disable GPS tagging don't stand to gain anything from this feature and as such would rather have it disabled, especially given the enormous load these scans put on the system. I had a look through the app settings but found no Maps entries, nor does the Settings option in the app itself allow one to disable photo scanning.

May I suggest the addition of such an option? It would make Maps usable where it currently isn't - yet I could have it finish the scan but that would take days if not weeks for no purpose whatsoever given the absence of GPS tags in the photos on this system. I jury-rigged the app to disable photo scanning for now so I can use Maps, if there is interest I can submit a PR for the requested features (i.e. global and/or per-user photo scan enable/disable)

No source file or test is named. Start by tracing photo-scan job creation and the Maps settings entry point, using the oc_jobs behavior described here; done means a global or per-user option prevents unwanted photo-scan jobs while Maps remains usable.