Update noteable after a new note is added

Created by: jvanbaarsen

What does this do? It makes sure that whenever a new note is added to a noteable item, the updated_at of that item is also updated.

Why is this needed? At this moment when you post a comment on an issue or add a label to an issue, the updated_at is not changed. Because of this the filtering for least recently updated is not really useful (since it only takes in account the original text from the noteable).