Certificates now list the words you built

Finish a volume and its certificate shows every word you solved —
the roots you assembled and what each one means. The free Sampler's
certificate also names which collection each word came from, and
how many more are waiting on that shelf.

Also in this update
- The SAT & TOEFL track is now called University Prep — same volumes,
  same words, covering the academic English that SAT, TOEFL, and
  IELTS all draw from
- The sound and vibration switches now sit in the header, within
  reach at any point in a puzzle
- The way back to the library sits with the volume name, just above
  the progress bar
- Small fixes to the bookshelf