break out functions from viewer into separate .js file(s)

[JonatanS]

To keep project more organized. This also helps adding functionality to specific functions (such as selection) over time.

[howesben]

@JonatanS - I vote yes please! Is there anyone else out there who prefers the one large .js file approach?

[theo-armour]

I also vote yes.

I have started this process in the R2 viewer I have started.