[New Feature] Tabbed navigation added to lesson (similar to quiz)

[New Feature] Tabbed navigation added to lesson (similar to quiz)
[Added] Graceful fails added to view.php, essay grading, and reports
[Changed] got rid of a lot of references to $_POST/GET/REQUEST
[Fixed] In reports, it required teacheredit, should only be teacher
[Changed] High scores - teachers can actually see them!  Also, improved output by using print_table and print_heading
[Changed] Grade essays now uses fullname() to print user names