AWS Cognito User Pool Management

- [x] Email template
- [x] The account email points to https://virtual.emnlp.2020.org which should be https://virtual.2020.emnlp.org instead.
- [x] The login instruction doc is [here](https://docs.google.com/document/d/1dGEUg5jNZwyK2w8RLhmgvz-DXq-Xu2_ezAveOYYZzY4/edit?usp=sharing), which you should adapt for EMNLP2020. You also need to update the link in the email.
- [x] The links to blogpost in the "Other useful links" should be updated
- [x] mailing list address (not sure if the capitalized EMNLP works)
- [x] Double check the password requirements. It seems that it only has letter + number, which should be good. There were some confusion during ACL2020 because we by default requires special characters so it would generate period, quotes which are easy to miss.
- [x] AWS SES configuration. The current email comes from `no-reply@verificationemail.com`. This is not going to work in practice. You should follow instructions [here](https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-email.html) to switch to the SES email.
- [x] You will need to register an email account. We used `acl2020virtual@gmail.com`, but you should double check with @desilinguist since we may be able to use `@aclweb.org` or `@emnlp.org`?
- [x] Don't forget to choose "yes" to "Do you want to send emails through your Amazon SES Configuration?", as indicated in Step4.6.
- [x] We didn't set a custom REPLY-TO address during ACL2020, but you might consider to add the helpdesk mailing list.
- [ ] Import registered users. A volunteer can probably be in charge of this.
- [ ] The code is [here](https://github.com/acl-org/acl-2020-virtual-conference-tools/tree/master/acl2020_tools/awscognito). You may need to adapt some based on the new EMNLP configuration.
- [ ] It also depends on the file format provided by Priscilla, so you need to check with her first to see how registration is handled for EMNLP2020.
- [ ] Handle registration during the conference
- [ ] We used Gmail forwarding + Zappier + AWS Lambda. There is no documentation, but we should be able to dig out the configuration on ACL2020's AWS account + Zappier account. This is relatively simple.
- [ ] This also depends on the registration company, so check with Priscilla first.

References (for my own record):
* https://github.com/acl-org/acl-2020-virtual-conference/issues/48
* https://github.com/acl-org/acl-2020-virtual-conference/issues/57
* https://github.com/acl-org/acl-2020-virtual-conference/issues/53#issuecomment-649327363