Prof/course IDs should be stable

[Josh-Cena]

Right now, imagine users opening the site & downloading the static catalog on day 1, then they keep the site open. On day 2, after a recrawl, they open a modal. The modal would then request related course info using the course ID / prof ID in the static catalog. However, it seems that after the recent rewrites, prof / course IDs are no longer stable, so this may end up showing unrelated courses. We should make sure that if a prof gets assigned an ID, it never changes over time, which means either a change to our ID assignment (which currently is just serial, based on whatever order the table has), or make our DB changes incremental, so only new profs get new IDs (much harder, see #303)

[Josh-Cena]

In 2c55cd8, the course/listing/prof/flag IDs are now stable. Evaluation data and the same-course component IDs are yet to be stable.