-fixed crash on getComponent when component doesn't exist

-fixed Components ids sorting
-added deferred object removing
-new EntityManager functions: begin(), end().

source/ecs/entity.d

@@ -21,6 +21,7 @@ struct Entity
     {
         EntityManager.EntitiesBlock* block = gEM.getMetaData(&this);
         EntityManager.EntityInfo* info = block.type_data;
+        if(T.component_id >= info.deltas.length || info.deltas[T.component_id] == 0)return null;
         return cast(T*)(cast(void*)&this + info.deltas[T.component_id]);
     }
 }