Const correctness

[Yelnats321]

Currently entities employ reference semantics rather than value semantics, which is the less intuitive of the two. This means that passing in a const entity to a function does not guarantee that the entity won't be modified (since you can just copy it into a non const entity and modify it there).

There are other problems like sync() not being able to be called from a const entity and other little things that just feel off.

The options going forward are either to keep things as is or to split entity into two classes, a const entity and a non-const one, where the manager will return one or the other based on context. Probably the best approach to this but might feel unintuitive and hard to follow.