Add application setting to restrict user signups to e-mail domains
This feature was requested long ago:
This MR is based off !253 (closed) but changed to use application settings and use wildcard strings to give more flexibility in pattern matching. Regexps seemed overkill and prone to mistakes.
Also note that validation is ONLY done on creation to prevent breaking existing users who do not have a whitelisted domain. However, this allows a user to sign-up and change his/her email to a non-whitelisted domain.
Screenshots:
