Add legal page with privacy policy and force routing to it under certain circumstances

Closes #203 (closed)

What does this MR do?

This MR adds a new module/page called Legal that will be used to show and accept an updated privacy policy.

Also, it enables forwarding a logged in user always and only onto the legal page until they accepted the necessary regulations.

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

Not at all

Links to related issues

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))