Styling changes for gradebook design improvements

Barbara needs more CSS classes for her work on MDL-47363
Seems reasonable to add those classes inside natural aggregation branch so she will (hopefully) only need to work with .less and .css

1. Add classes 'levelodd' and 'leveleven' (or 'depthodd' and 'deptheven') for cells in user report and setup page, and also make sure that 'level1', 'level2', etc. are added to each cell. This classes will be used for swapping background color for netsted categories and adding indentation to some fields. Add missing classes specifying which column cell belongs to, the table itself, the empty row, etc
2. Remove "Category total" row from setup page and move it's contents into the category header row. This will involve changing some behat tests checking the contents of the table.