Logic Simulator Update - Sub Circuits

I added many general improvements together with the additional feature of Sub Circuits.

Any circuit may be loaded as a Sub Circuit which appears as a part with inputs and outputs corresponding to the Input and Output pins of a saved circuit. Also, they may be nested i.e. used as a part of another circuit that is to be used as a Sub Circuit.

Under the hood, Sub Circuits are compiled from the loaded circuit, including nested Sub Circuits. So they reflect any changes made to their parent circuits.

Enjoy!