sorting functionality for username, firstname, lastname, and section on marks spreadsheet
adding sort_by cookie for grades
asc/desc works over pagination
sorting works with per page drop down
Jump to works only as for last name, so dont display it for other sorting orders
Fix indentation, and push ordering into get_filtered_items method
limit sorting to tas and admins
only display section for tas and admins
adding functional test for cookies in grade forms controller
Push sort and order into query. Fix line characters to 80
strip out uncessary fields in pagination helper
Merge pull request #928 from kiramccoan/issue894

Issue894: Marks spreadsheet: sort by User Name, Last Name, First Name, Section.
FIX for issue 915, added median, number of fails and number of zeros to dashboard