Automate OpenCellID import

[hannosch]

With #283 / #300 we added the code to import the OCID data from a local filesystem.

We should now automate this to fetch the files from the OCID servers.

This includes a new config setting for the OCID api key.

[Gitschubser]

The cellid data from MLS are maybe the next days available and would be imported to OCID too.
Question: Is that sure that the export from OCID (after import from MLS data) not included the own data from MLS too and then MLS import his own data twice?

[hannosch]

@Gitschubser OCID hasn't yet begun the work on importing the MLS data, this will follow later this year, so for now there's no chance of duplicating the data.

I imagine that once they get to this, they'll keep the data separate from the rest, so it can be easily updated and diffed with the latest MLS data.

[hannosch]

I'll leave this open until we add the schedule entry and have the api keys in place.