certify 6.x-2.0-alpha1

This is a major rewrite of the entire module, to allow submodules to expose new conditions. I have also done massive code cleanups (a lot of work was done more than one place in the code). During the alpha period I will try to be very responsive for issues regarding submodule support. This means that if you miss some API magic, I will try to push it out within 24 hours. :)

Both book and quiz conditions are separated out into submodules. Use them as a base for creating new condition types.

I have also added more classes to the HTML output, so the output should be easier to theme now.

NOTE: Please remember to run update.php after upgrading from 1.x!