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.
The kohana/core dependency needs to be updated now - kohana/kohana already uses the new 3.4-style modules call and you're about to add the kohana::init_modules call method which doesn't exist in 3.3. Dependency versions should be updated at the same time as the first commit that uses the API of the new version.

Re individual package versioning - that's maybe open to discussion. I think it's common in projects that provide a full-stack and a collection of individual packages (symfony, for eg) that the major version numbers are aligned to make it easy for end-users to set their own constraints.

Also a major version change of a package dependency is a major version change to that package - even if nothing else of the package API changes. For eg, if kohana/cache starts to require kohana/core 3.4 then that needs to become a new major release of kohana/cache. Otherwise end-users get hellish dependency conflicts - this is horribly common with minor version updates on ruby packages.