[bug 1068026] Switch the community hub to our global base.html

The community hub had it's own base.html with lots of duplicate stuff and not all the functionality you would expect on a SUMO page. This fixes that. I also make some styling tweaks to make the pages look a little better IMO. There is more that can still be done for sure.

Community hub is at /community. I'll post screenshots of the 3 pages in case you don't have the indexes set up to display nice data.

r?