Call render() when Icon is set to spin.

- When Icon used in Anchor widgets is set to spin, call render() to actually
  perform change. It's now same as setting Icon's position and other properties.
Merge pull request #207 from zlamalp/iconText

Call render() when Icon is set to spin.
Added setIconFixedWidth() and isIconFixedWidth() to HasIcon.

- Added option to set fixed width to Icon which is part of another widget.
  Other Icon properties were already part of HasIcon interface.
  Issue is covered in #208.