Merge in extension list plugin #121

I've been working on this plugin for a little while and it is in active development:
https://github.com/brashrebel/render-extensions-listing

As with many other popular plugins following the extension model, it is nice to present users with a convenient list in their dashboard of available addons. I believe that the ultimate user experience for this (as we've discussed numerous times) is to integrate with WordPress' add new plugins page. The approach is to simply add a new tab to that page called "Render" which lists plugins just like the others do except these plugins are coming from realbigplugins.com instead of w.org.

The plugin still needs some work to actually present all the needed information to the user and to integrate with the install process but I see the light at the end of this tunnel and hopefully a successful merge into Render once complete.