Website: Update Release Management for new Time Based Release Plan
Website: Update Release Management for new Time Based Release Plan

As discussed on the mailing list, I'm updating the BookKeeper website to reflect the new Time Based Release Plan.

You can find the staging website  https://aluccaroni.github.io/bookkeeper-staging-site/community/releases/

Please note that I've removed the calendar since it was empty

Reviewers: Enrico Olivelli <eolivelli@gmail.com>, Sijie Guo <None>

This closes #2251 from aluccaroni/master
apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,sijie/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper