Disable updater alerts and Check for Updates button on macOS

[thebodo]

Describe the bug
Optolith is not able to update itself.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Settings' (click on cogwheel in the upper right corner)
2. Click on 'Nach Updates Suchen'
3. Click on 'Aktualisieren'
4. The Dialog flickers
5. Click on 'Aktualisieren'
6. The dialog flickers OR an empty error message is shown (this might also take a third click on Aktualisieren)

Expected behavior
Update would start or at least a reasonable error message should be shown.

Screenshots

Environment (please complete the following information):

• OS: Mac OS 10.15.4
• Version: V1.2.0

Additional context
Add any other context about the problem here.

[elyukai]

This is a current limitation on macOS, since I can't code-sign and notarize the app right now. I have to disable those messages and the button, though, so that it suggests to do sth it actually cannot do.

I'm gonna change the topic that way.

Thanks! :)