Uniform foodsharing colors on the whole page

Closes #75 (closed)

What does this MR do?

Uniform colors on the whole page. does has been defined centrally in style.css as root color and then declared the individual colors as variable.

ToDos

• The CI green is 64AE24
• The CI brown is 533A24
• The CI beige is f1e7c9
• The CI white is F9F5E0

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

(be honest!)

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))
• 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