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above improvement this case is obsolete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)

tests/unit/functions/__snapshots__/updatenotification_spec.js.snap

@@ -11,24 +11,24 @@ exports[`Updatenotification custom module returns status information without has
 }
 `;
 
-exports[`Updatenotification default returns status information 1`] = `
+exports[`Updatenotification MagicMirror returns status information 1`] = `
 {
   "behind": 5,
   "current": "develop",
   "hash": "332e429a41f1a2339afd4f0ae96dd125da6beada",
   "isBehindInStatus": false,
-  "module": "default",
+  "module": "MagicMirror",
   "tracking": "origin/develop",
 }
 `;
 
-exports[`Updatenotification default returns status information early if isBehindInStatus 1`] = `
+exports[`Updatenotification MagicMirror returns status information early if isBehindInStatus 1`] = `
 {
   "behind": 5,
   "current": "develop",
   "hash": "332e429a41f1a2339afd4f0ae96dd125da6beada",
   "isBehindInStatus": true,
-  "module": "default",
+  "module": "MagicMirror",
   "tracking": "origin/develop",
 }
 `;