feat(core): split raw client and managed client as well as packet handlers

Resolves #65

fix(core): do not try to create stateful instance in case the entity is already present

fix(core): make stateful repository return the correct type

feat(core): add possibility to add items to stateful repository manually

feat!(core): make some classes internal

feat(core): add command pre and post events

feat(core): add stateful entities support

Supports injecting entities depending on the current nostale client.
Useful for remote, pipe client etc.