EPIC || USER ROLES: Default account type + optional activations for Teacher and Student roles

AC's:
- [ ] Ask right after sign-up what your role is **(ex. 1)** - one way to activate Teacher role
- [x] Ability to add roles later in Account Settings **(ex. 2)**
- [ ] Activate Student role by joining a class, via teacher generated URL **(ex. 3)** OR join a classroom manually
- [ ] You can be both a student and a teacher, and join your own class **(ex. 4)**

# ex. 1 (python room)
### Choose your role - appears right after signing up:

# ex. 2 (repl.it)
### Also option to add roles later in Account Settings:

# ex. 3 (repl.it)
### Teacher view - generating class URL:
## Student view - on clicking class URL:
# ex. 4 (repl.it)
### Ability to switch views based on roles: