Add email verification feature

[isabelcosta]

Description

Fixes #5
Fixes #7

Add email verification consisting of:

• Send an email to a newly registered user with a link with a token that verifies the user's email (updates is_email_verified and email_verification_date variables)
• Uses flask_mail extension
• Added tests to confirmation of email function on UserDAO
• Updated swagger.json
• Email confirmation token expires after 24 hours
• Email sensitive info is read through environment variables
• Updated the README informing of the necessary environment variables that should be exported
• The user should not be able to login unless the email is verified. In the attempt to do so, should receive a message saying Please confirm your email - Sent on PR Integrate flask-jwt-extended #64
• Define POST user/resend_email (no login required) sending new token. Body: {"email": }
• Update email template

Current email verification template:

Type of Change:

• Code
• Documentation

Code/Quality Assurance Only

• This change requires a documentation update (software upgrade on readme file)
• New feature (non-breaking change which adds functionality pre-approved by mentors)

How Has This Been Tested?

• Add 3 tests for the token confirmation function on UserDAO
• I created a test email because I need credentials to send emails on behalf of some entity (exported sensitive data into environment variables as explained on README)
• I’m registering users using temporary emails through https://temp-mail.org, to quickly test receiving verification emails (also I cannot use multiple users with the same email)

Checklist:

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials
• I have commented my code or provided relevant documentation, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged
• Update Swagger documentation and the exported file at /docs folder

Code/Quality Assurance Only

• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[Dilu9218]

Please resolve the conflicts :)

[isabelcosta]

@Dilu9218 merge conflicts are solved!