Fixes "Unable to locate a remote for" error

I had a problem with the url in git config not matching the tfs url due to differences in casing. After discussing this with Matt (@spraints) [here](https://groups.google.com/forum/?fromgroups=#!topic/git-tfs-dev/kiRE5FB5RKI), he came up with the solution of making the string comparison of the tfs url and the tfs repository path case insensitive (compared to the values stored in git config). 

I moved the current matching of urls from the TfsHelper class up a level to the GitTfsRemote class instead as the comparison is not coupled to TFS and could be more easily unit tested there.

There are unit tests for the GitTfsRemote class and integration tests for git tfs fetch/pull. I had to add some methods to the IntegrationHelper class to be able to run the git tfs fetch command and used libgit2sharp to count the number of commits before and after.

Hope this passes the :sparkles: test.