Opaque meta module + test - colorbar

[tech4GT]

(replaces #762) -- copying in description from there:

Re #315 -- an attempt to refactor the colorbar module to be a fully opaque meta module - that is, a module which:

1. contains other modules
2. acts like a normal module in every way
3. contains an independent sequencer in order to pass an input through a sequence and produce an output

If this works (and it's not running yet -- I'm stuck for some reason because draw() is not executing... help!) then we may be able to create a generator for these, which is to say, a way to automate the creation of opaque meta modules given:

1. a JSON object or string of steps
2. a function which maps the outer module options to the options objects of the internal steps (or falling back to the defaults if mapping is not provided)
3. a set of overriding defaults for internal steps (which could be done via the mapping function too)

@publiclab/is-reviewers take a look here, i got inspired and tried it out, but need a bit of help to debug my work!

[tech4GT]

@jywarren Actually there is no way of testing the options.inBrowser thing since we run the tests in node and inBrowser is false there anyway, haha.
Anyway I have fixed the condition and I don't think we need a test here, I tried all cases manually though. :)

Also I think we should resolve circular dependencies while dynamically loading a module into sequencer, thoughts?

[tech4GT]

Long term:
@jywarren I just had an Idea!! If we think scale we can bootstrap this sequencer inside sequencer idea to multiple image use cases like map-knitter, where we can initialize one instance of Sequencer for each image and run all of them as independent processes!!
Wouldn't this parallelize our workflow?? Eager to hear your thoughts!! 😃

[jywarren]

(re:#762)

Re parallelize, EXACTLY!!!

Re test, can we just do a looks_like comparison with a visually confirmed output image? I just think any test for colorbar would be good. Let's confirm this can be added as a step, it produces an output, and that output looks like a visually confirmed output image.

Re circular, I saw your comment and we can try that after this, yeah. Great!

[jywarren]

Also, what went wrong with this Travis build? Thanks!!

[tech4GT]

@jywarren Writing up the test and docs for this now!
Let's make the generator in another PR, also please do take a look at the optimizations pr!
Thanks!

[jywarren]

We should document this too!

[jywarren]

this is great, thanks @tech4GT !!!

[jywarren]

OK - now see: #765!