* Having a modal to manage filtering of assignments really didn’t make sense.  Now you can filter within the gradebook view. 
* Rerendering the gradebook after adding an assignment seems to take care of the disappearing assignment header. 
* Gradebook also rerenders on adding students, that way students are resorted according to last name.

git-svn-id: https://plugins.svn.wordpress.org/an-gradebook/trunk@1029867 b8457f37-d9ea-0310-8a92-e5e31aec5664