CLIMATE-452 - Add Unity desktop option to VM Build

- Add Ubuntu Unity option to OCW VM Vagrant build. By default XFCE is
  installed. If a user wants Unity, they should comment out the XFCE
  section and uncomment the Unity section when building the machine. It
  should be noted that the Unity install takes longer, but it comes with
  a lot more stuff out of the box (including looking nicer in general).