Add method to compare Tfs url and Repo path to GitTfsRemote

Moving logic from TfsHelper.Common and GitRepository into GitTfsRemote.
Easier to test as TfsHelper is tightly connected to Tfs and GitRepository is
difficult to test directly. Added tests for GitTfsRemote.
Add Fetch/Pull tests

Created tests for comparing the tfs url, legacy urls and
the repository path with mixed case when calling git tfs fetch or
git tfs pull. Used libgit2sharp to count the commits before and after.
Added support for running commands from the project directory (git
tfs clone is called from outside the project directory).
Merge pull request #277 from daniellee/tfsremotecaseinsensitive

Fixes "Unable to locate a remote for" error
Remove call to git command to set  config (use libgit2sharp instead)
Merge pull request #280 from pmiossec/remove_git_call_for_set_config

Remove call to git command to set config (use libgit2sharp instead)