add core UI component for on-off (boolean) component

[maks]

There is currently no UI component to represent a boolean state (on/off, true/false, etc).

On iOS this would be a switch

On modern Android this is also now a switch (historically in older, pre v4 versions they were "togglebuttons").

Following existing components I would expect syntax like:

{
  "type" : "switch",
  "text" : "switch label",
  "on_text" : "only on Android?",
  "off_text" : "only on Android?",
  "state" : "off",
  "style": {
    "on_colour" : "#00000",
    "off_colour" : "#00000",
    ...
  },
  "action" : {
  }
}