Show past community applications on community CFP page

[sagesharp]

The fix for #88 left the community CFP page in a bit of a mess. The time when I found this issue is when the application period is closed and no new round has been added. Right now, there is a list of past participating communities on the community CFP page. However, any community that hasn't had an approved participation isn't even linked on that page.

The impact is that there are some communities that are essentially hidden. They may be past communities that participated in Outreachy before the new website was created. They may have coordinators associated with it. When someone goes to sign up a new community, if the community name matches the name of a hidden community, they will get a very odd error when they reach the end of the community sign up form. (That's because the name is used as a slug and it must be unique across communities.)

We need a way to show these hidden communities. Perhaps break them into communities that were not approved to participate in any round and ones that are historic communities from before the new website?