Extend Space.eventSourcing.Aggregate from Space.domain.Entity

[rhyslbw]

Considering Aggregate is an Entity, and we're already dependent on space:domain, this will be a solid a change to make, and will also:

• Resolve the SnapshotType issue
• standardise the interface

@darko-mijic considering 3.0.0 isn't out yet, let's try to slip this in after some testing

[rhyslbw]

No point in rushing this, let's leave it for next time considering the current is stable and usable