Prior steps need not re-run when a new module is added or deleted

[jywarren]

In the demo, I see the entire sequence being re-triggered when a module is added or deleted.

We should only have to run the final new step, if a new one is added, and if one is deleted, only the steps after it. Let's look at the logic and if we need to make run() accept a parameter like sequencer.run(startIndex) we can do that.

[jywarren]

GitMate.io thinks possibly related issues are #27 (add fisheyegl module), #138 (Add a Dithering module), #157 (Add a Contrast module), #158 (Add a Saturation Module), and #113 (Add a Brightness module).

[tech4GT]

@jywarren Actually I also noticed this while working on the getStepApi, but this would call for some major changes in demo architecture or even in the architecture of the sequencer itself, I would suggest we keep this long term, what say?