Implement "Open" command
This MR Is the first try to implement the basics for a "Open" entry to open the webpage of the repo.
At the moment it is a basic implementation. It adds
TortoiseGitProc /command:open that does work the the remote
origin is on GitLab.com and GitHub.com. It is also possible to use the
/remote:name argument although there is no UI for this at the moment.
It adds "Open" to the main context menu. For some reason I didn't manage to test this until now. The tips in
src\Debug-Hints.txt don't seem to work for me, but I didn't want to hold back the MR.