Patch to make comments API more flexible and less dependent on the comments block

The attached patch is designed to make the comments API more flexible and usable by moving some of its hard coded options to proper options.
The hard coded checks for the comments block can then be replaced by checks for these options.
It also moves some of the smarts of the output function into separate functions.

This is required for the new plugins plugin (replacement for the modules and plugins database).

Cheers
Sam