Refactoring: ES6 rewrite

[estilles]

Hey guys!

I noticed a trend within the Companion community/ecosystem towards a migration to ES6. I had some free time on my hands over the holidays, so I decided to take a stab at it.

My PR I intends to accomplish the following:

• my first attempt at a general ES6 rewrite
  • separated the code into ES6 modules (index.js was getting a bit long)
  • moved everything into an src folder, just to keep everything tidy
• refactored the conversion to kelvin: A friend who is considerably more knowledgeable in lighting than I am pointed out the color temperature scale used by the Keylight (as well as many other lights) is called "mired". He also told me I don't need that long/ridiculous lookup table (yes, he actually called my code ridiculous), because I could mathematically convert from mired to kelvin (and vice versa). He sent me this link which explains it very well.
• added an upgrade script: Now that I can convert easily between and kelvin, instead of mapping multiple mired values to the corresponding kelvin value rounded up to the nearest 50, I simply used an upgrade script to fix existing mired values. I think this is a better way to handle the issue identified by @krocheck in this comment.

Let me know what you guys think.

[krocheck]

@estilles you think its ready?

[estilles]

@estilles you think its ready?

Yes. I've been testing it for the past couple of days and I think I've worked out all the kinks. :-)

[JTF4]

@krocheck we could create a new branch and merge the PR with that one if you want testing to continue.

[krocheck]

No that's fine, I was seeing the bugfixes coming in here so I wanted to get a sense of where we were at. I think it looks go, so we can merge this in.