(#2654) - new plugins and rename external page

Couple things:

* Renamed the "External Projects" page to just "Plugins." Given how many plugins there are compared to the other stuff, I feel it's more informative to the average user.
* Made an editorial decision to remove the [ember-pouchdb](https://github.com/taras/ember-pouchdb) in favor of my own [ember-pouch](https://github.com/nolanlawson/ember-pouch). I invite @taras to correct me if I'm wrong, but it seems that ember-pouchdb predates Ember Data and mostly solves the problem of PouchDB not having promises, which is a non-issue these days. To reduce user confusion, I'd rather just list one Ember module, but of course this it's open to discussion.