New: Add oSelectorOpts option for buttons to control which data is to be used from the DataTable

- The data get function has been rewritten to use the DataTables $
  method to get the rows that will be used for data output (copy to
  clipboard, save to file etc).

- The key reason for doing this is that the $ API method of DataTables
  has options to allow control the order or rows and what rows are
  included (paging and filtering). This is exposed as the new
  oSelectorOpts option.

- See http://datatables.net/docs/DataTables/1.9.4/#$ for the full
  options

- Example:

	$('#example').dataTable( {
		"sDom": 'T<"clear">lfrtip',
		"oTableTools": {
			"aButtons": [
				{
					"sExtends": "copy",
					"sButtonText": "Copy to clipboard",
					oSelectorOpts: {
						page: 'current'
					}
				}
			]
		}
	} );