String file cleanup

[Denz1994]

It was advised by @phet-steele to alphebetize this list of strings in the respective .json files (phetsims/masses-and-springs#151). I am relaying this suggestion along to @mbarlow12 for inverse-square-law-common-strings_en.json and coulombs-law-strings_en.json.

Also, consider changing to screen.macroScale and screen.atomicScale. Currently, the file reads like this:

 "screen.macro": {
    "value": "Macro Scale"
  },
  "screen.atomic": {
    "value": "Atomic Scale"
  },

[mbarlow12]

@Denz1994 thanks for passing along. I've made the changes; do you prefer closing issues you've opened?

[Denz1994]

You can close them @mbarlow12. They seem pretty straight forward.