MDL-25544 gradereport_grader: Improve Grader report user interface
MDL-46658 gradereport_grader: Update JS to meet coding style guidelines

This also moves the code into a set of separate files to allow for
additional components of the report to be migrated to the same YUI module,
adjusts some UI components, improves JS performance, and adds appropriate
documentation.
MDL-46731 gradereport_grader: Move tooltips to YUI module
MDL-46772 core: html_writer::table should respect tr attributes
MDL-46774 gradereport_grader: Move row/column highlight code to YUI module
MDL-46658 gradereport_grader: Remove old scrollview code
MDL-46658 gradereport_grader: Add user picture back to UI
MDL-46776 assignment: Add generation of assignments to the course generator