upower: show-icon config option

[czadowanie]

Adds the ability to hide the battery icon in the upower module. ie.

    "upower": {
      "show-icon": false,
      "hide-if-empty": false,
      "tooltip": true,
      "tooltip-spacing": 20,
      "format": "{percentage}",
      "format-alt": "{percentage} {time}"
   }

[Alexays]

Can you also add the option to the man and github wiki? :)

[Alexays]

Thanks!