Opt in

### javascripts/custom-repos.js
* Repos are now opt-in only
* Custom repos are now included
  * Defined by their full_name (e.g. `batmanjs/batman` from https://github.com/batmanjs/batman)
  * Each makes an extra API call
* Restructured file so the order is:
  * Shopify repos
  * Custom repos
  * Language overrides
  * Repo avatars

### General
* Removed duplicate repo count printing (now counts up instead of down too)
* Made sure repo homepage urls start with http (Batmanjs was simply batmanjs.org)