Add labels to a number of ct theorems and defns

They were missing them, and I want them for HoTTBook.v in HoTT/HoTT.
Merge pull request #653 from JasonGross/label-ct

Add labels to a number of ct theorems and defns
fix a misprint
add an erratum for the previous correction
Merge pull request #654 from DanGrayson/pull-2

fix a misprint
Mark Errata (auto)