Fix letterhead

A number of fixes to the LaTeX setup, particularly as they pertain to letterhead and the completion cert.  In particular:
* Remove the old MIT letterhead from the repo (we will need to upload the new letterhead to esp.mit.edu when this gets deployed)
* Set things up to compile to PDF and allow full-page PDF letterhead
* Fix some other issues in LaTeXed things

If other chapters want to use this, it should be fairly easy -- they can just upload a full-page or top-banner PDF letterhead to the appropriate directory, and everything should Just Work.