Fix code maturity, primarily our approach to Google Drive

This merge request will replace our now-obsolete Google Drive API calls with a simple call to open the Google Drive app. I can't find anything in writing to confirm this, but Drive appears to be a non-standard standard app on Android devices, and anyone doing field science using Google Drive would be well-advised (even without this merge request) to keep their data locally as well as in "the cloud".

I want to emphasize (for posterity) that there are real tradeoffs to this approach: we deliberately send users out of our own app into another over which we have no control, but in return we are no longer maintaining a lot of local Drive API calls and can focus field science development time on issues within the app itself. On balance I think that's the correct tradeoff.

Another commit in this merge fixes the other "Code maturity" warning from Android, which involved hiding the refresh icon when not scanning for devices. (I'm not sure this feature is currently visible.)

EDIT: This request addresses #29 (closed) ; clearer title.