Mass-change font Casks to use `version 'latest'`

This will bring the test suite in #192 much closer to passing.

The version numbers are preserved in comments so that they can be brought
back easily.  In many cases these are not really `'latest'` binaries, but checksumming
had to be disabled temporarily because svn downloads were inconsistent across
different filesystems.  (#118, still unfixed in the backend code).