Add input validation to wizard URL fields

If you paste an URL to the Git clone wizard, and the URL contains a leading or trailing whitespace, you get an error message like [1] after pressing Next.

It would be better to validate the URL before (like already done for the Path) and give a warning if it contains potentially invalid chars. A check for this is already implemented for Git RemoteAdditionDialog and would be nice to be used in the wizards also.

[1]

Klone nach 'qtserialport ' ...
fatal: Project not found: qt/qtserialport+
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.