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above improvement this case is obsolete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/node_helper.js

@@ -19,7 +19,9 @@ module.exports = NodeHelper.create({
 			}
 		}
 
-		await this.gitHelper.add("default");
+		if (!this.ignoreUpdateChecking("MagicMirror")) {
+			await this.gitHelper.add("MagicMirror");
+		}
 	},
 
 	async socketNotificationReceived(notification, payload) {