Pretty print error message on wrong credentials

[Zebradil]

Steps

• run the app with any incorrect credentials
• see the ugly stacktrace:

CRITICAL:root:('Invalid email/password combination.', PyiCloudAPIResponseException('Unknown reason'))
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/pyicloud/base.py", line 220, in authenticate
    req = self.session.post(
  File "/usr/local/lib/python3.8/site-packages/requests/sessions.py", line 578, in post
    return self.request('POST', url, data=data, json=json, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/pyicloud/base.py", line 110, in request
    self._raise_error(code, reason)
  File "/usr/local/lib/python3.8/site-packages/pyicloud/base.py", line 132, in _raise_error
    raise api_error
pyicloud.exceptions.PyiCloudAPIResponseException: Unknown reason

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/gimme_iphotos/__init__.py", line 81, in main
    DownloaderApp(vars(args)).run()
  File "/usr/local/lib/python3.8/site-packages/gimme_iphotos/downloader.py", line 106, in run
    api = self.connect_to_icloud(config)
  File "/usr/local/lib/python3.8/site-packages/gimme_iphotos/downloader.py", line 122, in connect_to_icloud
    api = PyiCloudService(config["username"], config["password"])
  File "/usr/local/lib/python3.8/site-packages/pyicloud/base.py", line 204, in __init__
    self.authenticate()
  File "/usr/local/lib/python3.8/site-packages/pyicloud/base.py", line 227, in authenticate
    raise PyiCloudFailedLoginException(msg, error)
pyicloud.exceptions.PyiCloudFailedLoginException: ('Invalid email/password combination.', PyiCloudAPIResponseException('Unknown reason'))