ENH: Support findPagingList() ... that uses firstRow & maxRows (rather than pageIndex, pageSize)

[rbygrave]

Currently there is:

query.findPagingList(pageIndex, pageSize)

This is ok but there is a desire/need to support using firstRow, maxRows instead. For example, in the case of continuous scrolling/paging ... the first 50 rows are fetched and then 20 rows after that as the user scrolls the UI (so maxRows is different from the first request to subsequent requests).

This enhancement will add support for writing:

// so this findPagingList() method with no arguments implies that 
// the firstRow and maxRows has been set on the query.

PagedList<..> pagedList = 
  query.where()
  ...
  .setFirstRow(50)
  .setMaxRows(20)
  .findPagingList();