Layout hooks for future control keys

In a previous commit, a framework was created for handling the
key-presses generated by the chess application.

In this commit, the framework is filled in with hooks allowing future
UI features to be tied in.  The feature hooks include pausing, undo-redo,
save-load, cancel move, etc.

These hooks are in the form of specific ascii and non-ascii
key presses in the key-press.c function handlers.