Use files generated from CoffeeScript

Some files (Timer.js, ImageData.js, Utils.js) were present both in bkcore and bkcore.coffee, and the the one in bkcore were used. This PR removes the redundant files from bkcore and modifies index.html to use the ones generated from CoffeeScript sources instead.

See also https://github.com/BKcore/HexGL/pull/23