Onboarding Improvements & GNU/Linux Auto-update

Improvements for GNU/Linux users:

• Auto-update works!
• Auto-launch on system startup too!
• The application should now be visible as expected on alt+tab.

Improvements for all users:

• Invalid cozy address detection was improved, including automatic detection of
  mycoSy.cloud with an s instead of mycoZy.cloud with a z (which seems
  to be a common mistake).
• The app also detects and prevent synchronizing your whole system or personal
  folder.
• Auto-update should be more reliable.

See known issues.

Happy syncing!