Give function GetComponentTypeName() const qualifier
Fix missing include
Create an EntityManager, IEntity interface and the FeatureID

EntityManager is in charge of requesting addition of features, i.e a
predefined set of components, to ECS. A vector of objects representing
components are returned by ECS.

EntityManager will fill the IEntity component map with objects returned.
These objects wrap a weak_ptr on the primitive data of the component.

Features are the new name of the metacomponents such as
PhysicalWorldLocation or ControllableMove. They contain each several
components that share the same lifecycle and are strongly dependant.
RigidBody now stores shared_ptr<btRigidBody> instead of btRigidBody*
Add Orientation and Body components objects.

RigidBody now returns a component to EntityManager when adding a body.