pointer entity template allocated by EntityManager. Can be null in which case empty entity would be added (entity without components)
list of components references to used. Memory form list replace data from template inside new entity. Should be used only for data which vary between most entities (like 3D position etc.)
Add entity to system. Returen pointer is valid only before one from commit(), begin() or end() will be called. To save entity to further use you should save ID instead of pointer.