Fauxton pagination using skip

This is a new version of pagination in Fauxton using skip. It uses a `PagingCollection` that has the main algorithm for pagination and exposes a nice api.

This is an intermediate step as this is a much better pagination than we have at the moment. However using just skip for pagination is not optimal as there are two cases where skip pagination fails - For very large skips and for when documents that a user have paginated past have been deleted. 

The next step once this has landed will be to add in a `startkey_docid` pagination as well. The PagingCollection would then decided which method to use to paginate for an index.