update file list with ajax so approval testing works better

Hi Jon,

I think the approval testing framework thing is working now. I'm using ajax to just insert or remove the new files, so it shouldn't affect the way other files are shown. The file "run_tests.js.erb" is a little more complicated now, and the "kata_controller.rb" run_tests method is starting to look messy. If you have any ideas for improvements, or general feedback on my code I'm very open to that. There aren't any automated tests for this ajax stuff I'm afraid.

Emily