Changed directory structure to remove SL from path. 

This is a backwards incompatible change, so it may be wise to keep it forked. The benefit is that the student-SL relationship is different than the student-Grader relationship. The grader for a student may change for specific assignments (i.e. Students moving sections or reassigning graders for a specific assignment). This has the added benefit of supporting future improvements towards the 198 program such as grading audits.

Because this change will make it harder for SLs to find the assignments they need to grade using scp/fetch, we also are providing a download link for them (see attached images).

As you can see in the images, Eric Yurko is an SL with no students. However, he has been assigned to grade Patrick's assignments for just a single assignment, Little Schemer. 

![Screen Shot 2013-01-06 at 12 55 24 PM](https://f.cloud.github.com/assets/1728051/46299/6fcc4ad6-5843-11e2-8eaf-e65d966faa48.png)
![Screen Shot 2013-01-06 at 12 54 20 PM](https://f.cloud.github.com/assets/1728051/46300/6fd11160-5843-11e2-873e-04d693651bc1.png)
![Screen Shot 2013-01-06 at 12 55 15 PM](https://f.cloud.github.com/assets/1728051/46301/6fccf8be-5843-11e2-8750-31123458a072.png)
![Screen Shot 2013-01-06 at 12 54 34 PM](https://f.cloud.github.com/assets/1728051/46302/6fcfe48e-5843-11e2-8359-64e998217cf1.png)