Let the common web user write to course data.

This is beacuse of hardcoded brokenness in how we deal with xml courses
right now.  The course has JS that is compiled when common.py is loaded
and relies on the DATA_DIR(course_data_dir) being in a specific relative
location to the edx-platform code dir.
Add the coffee binary to the path for edxapp.
Merge pull request #1436 from edx/feanil/compile_course_js

Let the common web user write to course data.