feat(widgets/stop_button): General stop button added

Description

Big red button which stops any running scan.

Related Issues

closes #222 (closed)

Type of Change

• New red button to stop scans

Potential side effects

Scary message pops up in BEC IPython client if scan was launched from there:

 BEC alarm:: An alarm has occured. Severity: MAJOR. Source: {'ScanWorker': '_process_instructions'}.
ScanAbortion.
	 Traceback (most recent call last):
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/scan_worker.py", line 748, in _process_instructions
    self._check_for_interruption()
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/scan_worker.py", line 645, in _check_for_interruption
    raise ScanAbortion
bec_server.scan_server.errors.ScanAbortion

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/scan_worker.py", line 765, in _process_instructions
    self._instruction_step(instr)
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/scan_worker.py", line 823, in _instruction_step
    self.wait_for_devices(instr)
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/scan_worker.py", line 129, in wait_for_devices
    self._wait_for_idle(instr)
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/scan_worker.py", line 513, in _wait_for_idle
    while not self.validate.devices_are_ready(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/device_validation.py", line 63, in devices_are_ready
    self.worker._check_for_interruption()
  File "/Users/janwyzula/PSI/bec/bec_server/bec_server/scan_server/scan_worker.py", line 645, in _check_for_interruption
    raise ScanAbortion
bec_server.scan_server.errors.ScanAbortion

Screenshots / GIFs (if applicable)

[Include any relevant screenshots or GIFs to showcase the changes made.]

Additional Comments

Function used:

def stop_scan(self):
     """Stop the scan."""
     self.queue.request_scan_abortion()
     self.queue.request_queue_reset()

Definition of Done

• Documentation is up-to-date.
• unit tests