Do not make unnecessary modifications to addedResources/removedResources

[krasnoukhov]

This fixes the case when persisting changes given there were previously loaded resources. Otherwise invalid requests will be sent in attempt to create already existing relations or to remove inexistent.

[krasnoukhov]

@wvteijlingen Please let me know if this change is ok with you so I'll update the specs

[wvteijlingen]

Good point! Wouldn't this achieve the same thing but in a bit more readable way?

public func addResource(resource: Resource) {
    resources.append(resource)
    if let index = removedResources.indexOf(resource) {
        removedResources.removeAtIndex(index)
    } else {
        addedResources.append(resource)
    }
}
public func removeResource(resource: Resource) {
    resources = resources.filter { $0 !== resource }
    if let index = addedResources.indexOf(resource) {
        addedResources.removeAtIndex(index)
    } else {
        removedResources.append(resource)
    }
}

[krasnoukhov]

Good point! Commit is updated with better implementation and specs.

[wvteijlingen]

Nice work! I'm not sure but I think we should assert addedResources.isEmpty in testRemoveAdded() and removedResources.isEmpty in testAddRemoved() as well.

[krasnoukhov]

Makes sense, commit updated

[wvteijlingen]

Sweet!