Javascript Fixes for Grader

I fixed two problems that were making the website not run on the live server

1) I removed ebookConfig.host (well set it to "") in layout.html because the admin page was getting screwed up by non-https requests

2) In admin/gradeassignments.html I replaced colons ":" from the username in a few places to allow jQuery to run. I think this is a quick fix, and ideally these characters need to be removed or we need to decide what auth_user field to use as foreign keys across models (it seems like ID and username field are used interchangeably)