Restore email uniqueness validation
Restore email uniqueness validation

+ Removed Devise :validatable because we no longer store user passwords because LDAP
+ But that removed email uniqueness validation too!
+ We don't want multiple Educator records with the same email address

erose/studentinsights,erose/studentinsights,studentinsights/studentinsights,jhilde/studentinsights,jhilde/studentinsights,jhilde/studentinsights,codeforamerica/somerville-teacher-tool,erose/studentinsights,codeforamerica/somerville-teacher-tool,studentinsights/studentinsights,jhilde/studentinsights,studentinsights/studentinsights,studentinsights/studentinsights,erose/studentinsights,codeforamerica/somerville-teacher-tool,codeforamerica/somerville-teacher-tool