added possibility to ignore MagicMirror repo in updatenotification (#3002)

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above improvement this case is obsolete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)

modules/default/updatenotification/updatenotification.njk

@@ -3,7 +3,7 @@
     <div class="small bright">
       <i class="fas fa-exclamation-circle"></i>
       <span>
-        {% set mainTextLabel = "UPDATE_NOTIFICATION" if name === "default" else "UPDATE_NOTIFICATION_MODULE" %}
+        {% set mainTextLabel = "UPDATE_NOTIFICATION" if name === "MagicMirror" else "UPDATE_NOTIFICATION_MODULE" %}
         {{ mainTextLabel | translate({MODULE_NAME: name}) }}
       </span>
     </div>