Add pagination to posts listing

* Add backbone-pageable plugin and use this to page the Posts collection
* Add handlebars-pagination helper
* Make pagination links dynamic
* Add events for changing page to the PostListView
Add 'total_count' to posts API - used in pagination
Update posts pagination with real totalRecords state

* use total_count from json in collection's parseState
* Trigger re-render of pagination on add/remove/reset of collection
  May not be the most efficient way to do this.
Prevent paging past first/last pages