Remove get_id/id functions.
ComponentManager: Remove unused function 'construct'.
ComponentManager: Remove 'using namespace std' from header.

Also take std::string parameter as const ref instead of by value.
ComponentManager: Replace references to deleted function.
Graphics component: Set default value of components to 0/null.
Rename Position to Transform; replace members with Box2D classes.
EntityManager: Major rewrite; use more templates where appropriate.
Update references to changed functions.
EntityManager: Replace #include with forward declaration.
EntityManager: Remove empty constructor/destructor.