Re-add signal code

Now we loop forever we need a way to exit after a CTRL+C
Limit hash size to 128MB

In case of high concurrency memory usage can quickly
climb with 256MB.

For instance with concurrency 4 we now use 1GB instead of
previously 2GB.
Teach worker to report crashes

For now do not differentiate between white and black.

Crash results will be saved in the db on host.