Updating parent entries is inefficient

[datenimperator]

A page part isn't searchable on its own, it only exists within the context of a page. However, editing text of a content page will most likely only update one or more of its parts. The page itself won't be updated, so the page's after_commit handler will never be fired.

Currently a page part will call page.update_index when updated or deleted. Updating more than one page part will lead to more than one invocations of update_index of the very same page, which is not very efficient.