Add appropriate listeners to all Entities

[Alrysc]

Listeners are added by the scene to Entities in the Mob when it starts. This means certain things, like counterhit and timefreeze actions, may not be applicable to Entities spawned after the scene begins.

See #3 (comment).

[TheMaverickProgrammer]

Recommended solution:

• Field broadcasts new entity
• Scene is responsible for filtering which entity is added to the pub-sub collection for battle-related callbacks such as counter hits.
• This flexibility allows automated identification of all entities, while still permitting the programmer to code custom behavior (PvE counter hits versus PvP counter hits).