Improved error handling when no match exists

matchbot now successfully raises a MatchError when no mentors are found.
Cleaned up API test script

Individual queries in flow_sandbox_test.py are separated into their own
methods for easier, more granular testing.
Adds basic per-run logging with rotating logs

Writes to a log file each time the bot runs.
Implements logging with the built-in logging module, with rotating log files
(eventual file size TBD). Does not log meaningful data yet.