was [requested in the
forum](https://forum.magicmirror.builders/topic/17519/updatenotification).
- added possibility to exclude MagicMirror Repo and renamed it from
`default` to `MagicMirror`
- improved getting `behind` in case a hard `git fetch` was already done
- removed test "excludes repo if refs don't match regex" because of
above improvement this case is obsolete
- improved `git fetch --dry-run` with `-n` option to exclude tags (noise
reduction)
