Cleaning up code, preparing to receive commands for execution. #1

Cleaned up unneeded or obsolete code. CmdTabPane.java is now the scroll pane
with the text pane hidden inside. The text pane will need to have document
listeners created. ALso, CmdTabPane.java will need to use those document
listeners to selectively enable editing - for instance, allowing edits only in the command area of the display.
Adding new message type (PROMPT) for sending a command prompt to the output. #1