Interact.py and Worksheet.py

Following the release of SAGE 3.1, I have began to work on published worksheets. The first thing I wanted to add was a "delete" button, but upon reading the code found no logical place to put the code for it - the HTML code in notebook.py is undocumented and very disorganized. So, to learn my way around I decided to first reogranize a bit.

Here is the header for a worksheet that I published.

Here is the same header on my development branch.

I'm not sure if anyone else will like this new header, but at least there is a logical place for the delete button, both in the UI and in the code.