Preen mocha and chai. todo: fix concat
Make the concat list explicit

Since I decided to preen mocha and chai, we can no longer generate the
concat file list from the preen config. We must instead explicitly list
the modules we want to concatenate. I placed this config in bower.json
so that most of the time, we won't need to change the Gruntfile.

Also added a concatenation task for test page dependencies.
Grunt Clean to remove node_modules

if you run "grunt clean" it'll remove the node_modules sub-folders
(remoov. Useful for people who install things via bower, as it produces
an error when trying to load the Chrome extension.
Updated the readme to include new grunt clean stuff.