Add a way to reset the database

[2opremio]

We should have a mechanism to reset the database. This could be done are a result of a version change #197 or manually, as an emergency measure (in case an inconsistency is found on the database).

Resetting will happen on startup either proceduraly or through a command-line flag properly marked as dangerous.

Since this is risky, the exact UX to use when doing it manually should be discussed and with ops.