Added dotenv development dependency
Allow a single Course to be active at a time
Force DM auto_migrate after each test is ran
Force an active course if none is available
New current_course was not being set
Auto assign Courses to Accounts on creation (and vice versa)
Call dotenv only if available on environment
Nullifying current course from session's data
Merge pull request #83 from fiuba/active_course_fix

Keep a single active course