enhances database actions activity for small screens, fixes a related crash

One of the few activities and fragments that still suffers on small screens is database actions. This merge request goes a long way to fixing that. Cleaning and erasing buttons are consolidated into a popup menu accessible by touching "Clean or erase". The smaller set of buttons fits comfortably into two rows rather than three or more.

This also patches a bug. Previously, we were not resetting the global trip name setting when erasing the database. That meant that when a user tried to collect data, the app thought there was an underlying database, and therefore did not prompt the user to set up a fresh database, and therefore failed to initialize the site and sector on the sampling activity, and therefore crashed. The trip name now correctly clears when we erase the database.

These changes are fairly well-tested as a matter of functionality, so I'll merge immediately after posting this.

Related to #11 (closed). Consider closing.