A load of composer fixes

* I've added some missing dependencies to the main composer.json file that were present in the subsplit repos, and added a couple of missing dependencies to the subsplit repos.
* I've alphabetically sorted the dependencies, and corrected their version constraints (nb. I raised twig that high to avoid a security vulnerability present in 1.0-1.12 of twig).
* I've added the correct "replace" composer attribute.
* I've updated the autoloading in the components to be the same as what I did for Laravel 4.3.
* I've added branch aliases everywhere (I aliased the master branch so the dev changes come from there rather than the master branch, thus matching the behaviour you have in the other repos).
Not anymore. I switch the components to psr-4 autoloading. It avoids hacks like that. I did it to laravel/framework a while back: https://github.com/laravel/framework/commit/230f25c421da51388fc62049b910112c75ef0170.