Add support for using existing named remotes

I wanted to add some tests to check the regex, but I couldn't get the `grunt test` task to run locally. That said, I tried the regex against a number of possible names to make sure it worked.

No matches
------------------
origin
weird$1+name
remote_name
remote_name_extended
remote-name
remote.test

Matches
------------------
/path/to/repo.git/
path/to/repo.git/
/path/to/repo
\path\to\repo
path/to/repo
C:/user/repo
file:///path/to/repo.git/
git://git.com/~user/path/to/repo.git/
http://git.com/path/to/repo.git/
https://github.com/user/repo
ssh://user@server/project.git
user@server:project.git

closes #24