R1:a5f8846f472b

Use a unique random key to identify queries, not a sequential ID

Summary:
We save search information and then redirect to a "/search/<query_id>/" URI in
order to make search URIs short and bookmarkable, and save query data for
analysis/improvement of search results.

Currently, there's a vague object enumeration security issue with using
sequential IDs to identify searches, where non-admins can see searches other
users have performed. This isn't really too concerning but we lose nothing by
using random…