Finding Ground/Neutral Wire in Switchboard
I don't believe there's a neutral in this box.  I say this because neutrals are generally not switched, and as far as I can see every wire in the box is connected to a switch terminal (except the grounds).  

The bundle of bare wires twisted together capped with a yellow wire nut are grounds.  Grounds can be bare or green.  

This will be a problem.  the instructions for this device state a neutral is required.  

There are a couple wiring issues there, bit of a train wreck overall, the two screw terminals on the switch are wrapped the wrong way, counterclockwise rather than clockwise, and the white one in particular looks like it's not too solid.