Add the ability to add woff2 files to the docker

Summary:
To complement pull request #142, add the ability to automatically
generate the woff2 files from within the docker. Add a script for copying out
the generated font files to make things easier. Remove the KaTeX_Greek font
files as well as the KaTeX_Win ones, since we don't use them and they're oddly
non-woff and non-eot specific?

Test Plan:
 - Build a new docker from the new Dockerfile
  - Make sure the woff2_compress program compiles
 - Follow the instructions in the README to build the fonts
  - Make sure the fonts correctly build
  - Make sure the copy_fonts.sh script copies the fonts out

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D13637