Add changelog page, markdown parser, menu entry
What does this MR do?
Adds a changelog page using the very simple content page view.
That renders the CHANGELOG.md file with a markdown parser.
How confident are you it won't break things if deployed?
Links to related issues
- 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))