Show achievements on the user profile page

Makes a few key changes to the way achievements will end up working:
 - Rather than store achievement definitions in the DB, they're stored as a static list in code.  A few sample achievement definitions were added.
 - Achievements were moved into the user app, and the `achievement` app was renamed to `quiz`

Also fixes an issue with the gulpfile image copying (which I noticed after I added our first image).
It turns out that unsurprisingly, `makemigrations` can't figure out it should delete stuff from the `achievements` app after you rename it to `quiz`.  I'm inclined to leave the orphan tables there.