Add a reset command to be able to reset a remote to a previous commit

to fetch changeset again.
Rename to ResetRemote
Use the '--force' option to force git-tfs bypass optimisation preventing fetching again the changesets

and add a help message on the 'reset-remote' command
help on the 'reset-remote' command with some use cases
Merge pull request #443 from pmiossec/reset_remote

Add a reset command to be able to reset a remote to a previous commit