R1:5aae1ee034ab

Make query panels editable by normal humans

Summary:
Ref T4986. Instead of requiring you to know engine class names and copy/paste URLs, provide select dropdowns that use SCARY JAVASCRIPT to do magical things.

I think this is mostly reasonable, the only issue is that it's hard to create a panel out of a completely ad-hoc query (you'd have to save it, then create a panel out of the saved query, then remove the saved query). Once we develop T5307 we can do a better job of this.

Test Plan: See screenshots.