Provide warning before unlinking repository #581

Is your feature request related to a problem? Please describe.
It happend to me a few times that I accidentially unlinked a repository using the button in the GUI. I was a little bit surprised that no warning appeared, and think this is caused by the fact that the "Unlink repository" triggers an action that takes at least a little effort to undo (i.e. looking up the repo URL, passphrase, etc.) and that I am somehow used that software warns me before such an action is performed (though I technically have the full responsibility for clicking the button, it just feels like a behaviour I am used to).

Describe the solution you'd like
Implement a warning before the repository is unlinked, i.e. "Do you really want to unlink the repository? No data is lost, but you have to manually enter all the information again to undo this action."

Describe alternatives you've considered
Don't change the beaviour and have the user take the full responsibility for their actions ... ;)