Added new CmdTab.java class that will represent text display+input.

Need to:
1) Create a new CmdTab instance in CmdTabMasterFrame.java when a new tab is
   needed;
2) Link CmdTab instance to TabbedCmdController.java as action listener for when
   a new command is entered;
3) Have TabbedCmdController see which CmdTab produced the Event and send the
   input text to the associated CmdProcess.
Running hard-coded commands now works. Issue #1.

Next, make it so you can enter arbitrary commands.