Teardown broken databases temporary for repairing

[oleiade]

Implies the usage of a dedicated repairing worker.

The process should look like this :
* Client sends a request, which raises a LevelDBError Corruption
* The worker which received the request, responds with a CorruptionError, extracts the db for the DatabasesHandler, calls for the repairing worker, and wait for it's completion (When the db has been repair, it should be put back in the DatabaseHandler).
* When the repairing worker is done, it reinserts the repaired db in DatabasesHandler, and closes
* The worker which received the request detects the db has been put back in DatabasesHandler, sets it self up again.