Fixed stepping

Added comments to LMC_Client.

Give step notification before execution.  Make sure notification is given for all steps.

Don't allow blocking on output.

Allow specifying the width of a Register entry field.  Provide a set() method that takes an integer and displays it with the proper number of leading zeros.  Show a green light in the input field when the program needs input.

Indicate the memory cell of the current operation with a filled progress bar.  Update the memory display on each step.

Show the accumulator register.
Add icon display to Register

Replace "width" parameter with "icon" bool.  The width is calculated automatically.  If "icon" is true, set_ready() can be used to show or hide the icon.