Implemented changable icons for AppleScriptTouchBarItem

[FedorZaytsev]

AppleScriptTouchBarItem now allow to specify any number of icons which can be changed from the script.

To do it, you need to return an array of two elements {"TITLE", "ICON_NAME"} from apple script instead of just a string with title. When array is returned, we take second element of the array, pick the corresponding icon from "alternativeIcons" and update it.

Example of usage:

{
    "type": "appleScriptTitledButton",
    "source": {
      "inline": "if (random number from 1 to 2) = 1 then\n\tset val to {\"title\", \"play\"}\nelse\n\tset val to {\"title\", \"pause\"}\nend if\nreturn val"
    },
    "refreshInterval": 1,
    "image": {
      "base64": "iVBORw0KGgoAAAANSUhEUgA..."
    },
    "alternativeImages": {
      "play": {
        "base64": "iVBORw0KGgoAAAANSUhEUgAAAAAA..."
      },
      "pause": {
        "base64": "iVBORw0KGgoAAAANSUhEUgAAAIAA..."
      }
    }
  },

This element would randomly change it icon from alternativeImages["play"] to alternativeImages["pause"] and back.

All old script would still work as before.

[FedorZaytsev]

Probably a solution for #268 and #216

[Toxblh]

https://github.com/Toxblh/MTMR/runs/475849335?check_suite_focus=true

Can you pls fix test?