Reorganize modules with backwards compatibility
Reorganize modules with backwards compatibility

So that `include AggregateRoot` does in fact `include
AggregateRoot.with_default_strategy`.

This opens possibilty to pass different strategies already on include.

Also this shows intent of coupling on_methods with default strategy,
there is no use of them for other strategies (without relying too much
on internals).

RailsEventStore/rails_event_store,mpraglowski/rails_event_store,arkency/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,arkency/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,arkency/rails_event_store,arkency/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store