Convert widgets to classes

[ethernian]

Looks like widget should become their own instance properties like label or state.

• introduce widget as classes (Button, MenuIem, etc.).
• unclear: are there any static members of the WidgetClass? Changes affect all instances...
• make widgetConstructors return an new instance of the class.
  https://github.com/dapplets/typescript-examples/blob/8135cbf98f5b39ce883938c1897dcc1b36367cca/packages/twitter-adapter/src/widgets.ts#L3-L10

Example of configuration items becoming instance properties:

button({ // `this` is bound to the button instance
    class: 'dapplet-tweet-south-metamask',
    img: { //ToDo: programmatic keys per-generator? [key]
        ready: METAMASK_ICON_READY, 
        running: METAMASK_ICON_RUNNING, 
        disabled: METAMASK_ICON_DISABLED
    },
    exec: (ctx: any) => this.state == "ready" && Core.sendWalletConnectTx('1', ctx)
          .bindTo(this.state); //binds connection state state to button's one.
    //...  more properties
});