Set up Mesh object and default unit cube Mesh

The default mesh will be set for any Visual component that doesn't
otherwise have a mesh name set.
Convert entity component list to a map

The common case is to pull out a component by type, so making this an
O(1) operation. I haven't thought of a situation where I'd want to
iterate over all components on an entity from outside of said entity.
Start building a Renderer interface and updating game initialization

This also includes building out handling of Meshes and starting hooks
into loading graphical data into the OpenGL subsystem.