Clean up usages of createObservableArray.getArray

[samreid]

As described in #266 (comment)

I improved documentation in the commits. I noticed there are 86 occurrences of .getArray() across the codebase. Many of these could be converted to use ObservableArray.filter and ObservableArray.map which were improved in #265 or other ObservableArray methods. Others may have simple solutions, and the ones that remain should be documented accordingly as prescribed in #266 (comment). For example, density and buoyancy has:

return _.find( this.masses.getArray(), mass => mass.isBoat() ) || null;

But this could likely be changed to something like:

return this.masses.find( mass => mass.isBoat() ) || null;

I'm not sure who should work on this or when it should be done. Should this be a chip away issue, so each developer can edit and test their own sims? @ariel-phet what do you recommend?

[samreid]

In the preceding commit, I implemented one of the conversions. I first ran the code to make sure worked correctly, and that I could understand when it was being called in the sim. Then I converted usage, and added a console.log() to double check the new code was being run in the sim. I removed the console.log before committing. When committing, I referenced this issue URL so the change is easy to track.

[ariel-phet]

@SaurabhTotey -- @samreid committed an example above for you to follow. Probably have a brief conversation with him if you get a chance to do this work.

[samreid]

ObservableArray has been deleted. Let's repurpose this issue for removing usages of createObservableArray.getArray(). Be careful not to remove any calls to PhetioGroup.getArray().

[samreid]

I removed usages detected through aqua, as well as the getArray itself. CT may find other cases. Closing until then.