FR: Toggle power-user search in search page

It's great to be able to set the power-user search on / off. But it would be better to use that as a default, and allow the user to toggle advanced search on the search page directly. Most of the time, I want it to be simple... but sometimes, I need extra power (especially when I want to make a bookmark, e.g. for all items not in a folder) and would love to be able to toggle it on.

Since the simple query already allows you to choose between what you search, it would make sense to add a third option "Advanced" there.

Start at the search page and inspect how the simple query options and the existing power-user search setting are connected. The change is done when Advanced appears as a third search option and users can toggle it directly while simple search remains the default.

Written by the indexing model from the issue text.