Ref T7803. Ordering and paging are inherently intertwined, but they often aren't driven by the same data right now.

Start driving them through the same data:

• getOrderableColumns() defines orderable and pageable columns.
• getPagingValueMap() reads values from a cursor.

This is generally sufficient to implement both paging and ordering.

Also, add some more sanity checks to try to curtail the number of ambiguous/invalid orderings applications produce, since these cause subtle/messy bugs.

• Paged through pastes and a few other object types.
• Intentionally changed defaults to be invalid and hit some of the errors.