Fix/adam/lms help button

Fixes various issues with the help modal:
1) broken JS was causing multiple divs to show up, which was 
   a) ugly: https://edx-wiki.atlassian.net/browse/LMS-869
   b) causing disgruntled students repeatedly to click submit, creating many duplicates of issues, creating headaches: (https://edx-wiki.atlassian.net/browse/LMS-854?jql=text%20~%20%22help%22)

2) Has the faq link point to the marketing site's faq if there's a marketing site. Otherwise to the LMS's /help page.

3) adds a dummy FEEDBACK_SUBMISSION_EMAIL to lms/envs/dev.py to help with debugging the modal

@gwprice @cpennington