Allowing multi-collection searches?

[rudexi]

Currently, some multi-collection searches are not possible in our system.
One typical use-case is the following: Show all alerts that a certain person acknowledged.
Since the comment and record collections are separate and one reference the other, it's not possible to do this search.

The concerned collections are:

• record and comment
• * and audit

No clue how to do that in term of web interface. That is out of scope of our query language for now, and this has the potential to bypass permissions if it's implemented too broadly.