Add end-to-end unit-tests verifying enforcement of access control during
conflict resolution.
Implement two facade methods providing REST API for Change methods used
by conflict resolution:
PersistedModel.findLastChange
GET /api/{model.pluralName}/{id}/changes/last
PersistedModel.updateLastChange
PUT /api/{model.pluralName}/{id}/changes/last
By providing these two methods on PersistedModel, replication users
don't have to expose the Change model via the REST API. What's even
more important, these two methods use the same set of ACL rules
as other (regular) PersistedModel methods.
Rework `Conflict.prototype.changes()` and `Conflict.prototype.resolve()`
to use these new facade methods.
Implement a new method `Conflict.prototype.swapParties()` that provides
better API for the situation when a conflict detected in Remote->Local
replication should be resolved locally (i.e. in the replication target).
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