Add Remote: better default name of remote from URL

If a remote from GitHub is added always the last part of the url, which is the repository name, is used. If you want to add another fork to modify the branch as maintainer of the forked repository I always need to change the name.

E.g. for GitHub it would be better to not take the last part, e.g. instead of https://github.com/Spacetown/gcovr it would be better to take https://github.com/Spacetown/gcovr or the last two parts.