Enclose custom data sets in collapsible panes when they are included in Report Criteria Display Columns and Filters

Modify Report Criteria "Display Columns" and "Filters" sections to render custom data sets in collapsed panes for Display Columns and Filters section.

Fix CRM/Report/Form.php to sort custom data sets by Weight (currently sorted by table_name for some reason??).

Thanks for Eileen McNaughton for her foundation work on this issue!

NOTE: In order for custom fields to be included in a report, the report's PHP class file needs to define the $_customGroupExtends variable. Several reports already have this defined (including Donor Report-Detail and Constituent Report-Summary). Currently inclusion of custom fields in the reports does not respect permissioning. I have filed a separate issue for 3.3.1 to fix this and modify most of the other reports.