Remove student login functionality

[derekdotdev]

Remove student entity, login function, username from top right corner of "student" templates, and survey/session dependency on student id. Instead, of getting zip code via student id, we will ask for zip code in the survey. Doing this will remove the ability to access prior survey results and resources until another method is devised, but will ultimately ensure the greatest amount of anonymity for those who are taking the survey.