Add Cursor based pagination.

[tomchristie]

With 3.1's new pagination API the initial styles will be PageNumberPagination and LimitOffsetPagination.

We should also add an CursorPagination that uses cursor based pagination for use with very large data sets, where indexing into the result set is infeasible.

However, let's not let this block the 3.1 release - we'll slate this for 3.2 instead.

[samrad]

+1 Tom.

[tomchristie]

For reference: http://cramer.io/2011/03/08/building-cursors-for-the-disqus-api/

[tomchristie]

Also http://www.sitepoint.com/paginating-real-time-data-cursor-based-pagination/

[maryokhin]

This is great and is really needed!

[tomchristie]

Bumping to 3.1

[tomchristie]

Now in the version-3.1 branch.

Few tweaks to follow up on being tracked against #1169.