Big changes to GUI - Buttons, wiring, property edits

Create mode
   Left click to create a component
   Right click to delete a component
Wire mode
   Left click on a component to select the input, then
   left click on a component to wire the input to the selected output
   Right click on a component to disconnect an input
Edit mode
   Left click on a component to open a dialog to change its properties
Update mode
   Left click on a component to update its inputs and outputs

Step button - Do a single update on the circuit
Run button  - Repeatedly update the circuit (by default every 500 ms)

Removed the 'Circuits' root from the component selector

Some other changes