[Core] Separate DI container from Mannequin itself

[rbayliss]

Using Silex for the DI container, the HTTP application, and the kernel. As we start to think about more extensions, we're going to want cleaner separation of those things so they can be tested and extended properly, and evolve without breaking BC. So let's split the DI container and the HTTP application out of the Mannequin class and just use that class as the Kernel to bootstrap the container. A ContainerInterface has already been defined - this is just a matter of creating a separate concrete implementation, then adjusting extensions so they receive the container instead of Mannequin.

[rbayliss]

This seems unnecessary at this point. Closing.