See: !1309 Refactor register form to multi step pages in vue

• Closes #540 (closed)
• Closes #680 (closed)
• Closes #723 (closed)
• Closes #653 (closed)

What does this MR do?

We have a lot of support tickets where users can not fully complete the registration.

1. With the help of @alangecker commit the register form is built in vue.
2. HTML template in RegisterForm.vue extended with all fields
3. The address search removed because implementation is not so easy and after consultation in the dev channel as a foodsharer is not necessary.
4. Use contentGateway for legal info.

Which fields should be mandatory fields?

• E-Mail
• Password (minimum length 8 characters)
• First given name?
• Gender
• Surname?
• Date of birth?

ToDos:

• A working validation for page 1 (mail and password)
• A working validation for page 2 (firstname and lastname)
• A working validation for birthdate
• Redirect to login form after a successful register.
• Remove old register code
• Remove old validation code
• Create php unit tests

How confident are you it won't break things if deployed?

I'm not sure since I'm still a beginner. However, it was very tested by @jofranz @fs_k.

Links to related issues

• #540 (closed)
• #680 (closed)
• #522 (closed)
• #241 (closed)

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. Click to "Mach mit!"
3. Click to "Jetzt registrieren!"
4. Fill field "E-Mail"
5. Fill field "Passwort"
6. Fill field "Passwortwiederholung"
7. Click to "weiter"
8. Click to a gender
9. Fill field "Vorname"
10. Fill field "Nachname"
11. Click to "weiter"
12. Fill field "birthdate"
13. Click "weiter"
14. Fill field "Handynummer"
15. Click to "weiter"
16. Check option "Rechtsvereinbarung"
17. Check option "Datenschutzerklärung"
18. Uncheck option "Newsletter"
19. Click to "Anmeldung absenden"
20. Check your inbox for registration mail
21. Click to "Anmelden"
22. Test the first login

Screenshots (if applicable)

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings