If the user wants to register a new account we check whether the
provider allows registration or not right after getting the
provider.json file and show an error msg on the wizard if not allowed.

Also, there is a new signal to handle the error raised by the server if
a registration attempt is made but is rejected with error 403.

- Resolves: #6594

Register to Soledad's sync (send and receive) events and display the
progress in the UI.

- Resolves: #7353

Also, do not raise assertionerror, log warning instead.

- Resolves: #7284

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