Prevent locks caused by the zmq log handler reaching the zmq's HWM (High
water mark / buffer limit) and causing some components to block until
the buffer is empty (running the zmq handler for instance).
We run the zmq handler in the background all the time to prevent this.

- Resolves: #7222

Replace logging.getLogger with custom get_logger.
Remove some unneeded dependencies and reorder other.

- Add a new handler for a zmq/thread-safe log send between components.
- Update the log window to use this new handler.
- Remove old custom handler
  We have implemented a new handler that uses logbook, so this one is no
  longer needed.
- Adapt log silencer to new handler
- Use log file always as default

- Related: #6733

- Related: #6359

Before this commit, the backend used plain pyzmq bindings for communicating
with the frontend. This implements the txzmq twisted-powered bindings instead.

Closes: #6360

If the quit() call is triggered by the system logout we should not
disable the autostart. Otherwise bitmask won't autostart on the next
session start.

- Resolves: #6424

Catch the keyring.errors.InitError exception.
The automatic login sequence now stops correctly instead of freezing if
the user cancel the keyring open operation.

- Resolves: #6682

After a provider fails to pass the checks, the providers combo box is
not enabled when it should, we just took care of the provider line edit.

- Resolves: #6418

Also set text to 'bold' so it's easier to find at a first sight.

- Resolves: #5526

FIX: Login attempt is made against previously selected provider.

Closes #6654.

Cherry-picked from release/0.8.x since it's a very annoying bug for the
testing cycles for the next release (0.9.0) -- kali.