388 verify account v1

[jerohero]

closes #388

What is it supposed to do
Implements the account verification flow, generating a verification link after registering. It creates a verification entity for an account when it is registered, and deletes it when the generated link is visited. The link is functional, but is not sent to the user's email address. A temporary button with the link is added so you can actually verify.

How can we test your branch
DB was updated so do npm run reset first. Register an account, after which "verification email sent" should be shown. Click on the temporary verify button, which should verify your account and sign you in and redirect you to your new profile. If you go to the link after the account has been verified already (or the code is incorrect), a message should appear stating that the code is invalid.

1. General checklist

• [x] a. Tested happy flow.
• [x] b. Tested unhappy flow.
• [x] c. No unexpected exceptions.
• [x] d. No code with high complexity. (Big O)
• [x] e. EOF newline.
• [x] f. No linter warnings or errors.

2. If relevant, front-end checklist

• [x] a. Responsive. (Desktop all the way to mobile 320px)
• [x] b. Using SCSS variables where relevant.
• [x] c. Relevant class names
• [x] d. No modified global SCSS properties, except if necessary and fully tested the impact.
• [x] e. Checked caniuse for more modern CSS properties.

3. If relevant, back-end checklist

• [x] a. No unhandled promise rejections.
• [x] b. Seeders still functional.
• [x] c. No primary-key violations.
• [ ] d. Normalization, at least 3NF.
• [ ] e. Used guards (middleware) where necessary and tested if route is guarded.

4. If relevant, test these browsers

• [x] a. Chrome
• [ ] b. Firefox
• [ ] c. Opera
• [ ] d. Edge
• [ ] e. Safari

[jerohero]

Just to clarify, this PR does not implement any of the points in the alpha 1 checklist.

• Emails are not sent
• Attempts are not tracked
• Expiration date isn't handled (for now it's just the current date, as it's not used)

[jerohero]

New error when trying to log in when the user has not been verified: