Add CompositeStepper

[dangthaison91]

For some situation, I have both VM and ViewController act as Stepper. Navigation will be driven by business logic from VM and presentation logic from ViewController. CompositeStepper will help to combine multiple Steppers.

This PR is WIP:

let createScheduleViewController = CreateScheduleViewController()
let createScheduleViewModel = CreateScheduleViewModel(id: nil)
root.present(navi, animated: true, completion: nil)
return [Flowable(nextPresentable: createScheduleViewController, nextStepper: CompositeStepper(steppers: [createScheduleViewModel, createScheduleViewController]))]

[twittemb]

Hi @dangthaison91

Now that the subscriptions are flatten in the Coordinator (branch develop), do you still want to introduce a CompositeStepper ?

If not, I will cancel this PR.

Thx.

[dangthaison91]

@twittemb I will test this again by today.

[twittemb]

Hi @dangthaison91

I am reviewing / testing your work. I will keep you in touch.

Thanks.

[twittemb]

I have 3 remarks:

• please rebase your branch on the current develop because I just made a fix that allows your code to work
• CompositeStepper is defined 2 times
• Rename your PR to remove [WIP]

After that we should be good to go

[twittemb]

CompositeStepper is defined 2 times

[twittemb]

Thanks @dangthaison91