Fully integrate composer

This PR makes it so Kohana modules must be installed using composer instead of using git submodules. 

Modules with the composer type of "kohana-module" are forced to be installed into the standard vendor directory.
We're looking to remove all global constants from Kohana, we definitely don't want to add another. Consistency shouldn't be an issue, I plan to deprecate APPPATH and SYSPATH in 3.4.