renaming some classes and using the octave namespace in the GUI

[John W. Eaton]

We have a variety of class names in the GUI that are inconsistent and 
that I think are a bit worse than they could be.  For example, we have 
variable_editor (OK) but terminal_dock_widget (not so OK).  I propose 
the following changes to better reflect the purpose of each object and 
to drop the suffix that indicates the type of Qt object that we are 
inheriting from:

  doc_browser, not documentation_dock_widget
  file_browser, not files_dock_widget
  history_browser, not history_dock_widget
  command_terminal, not terminal_dock_widget
  workspace_browser, not workspace_view

I'm not sure about command_terminal.  Is there something better?

We are also inconsistent in the names passed to QObject::setObjectName. 
For exmaple, we have things like HistoryDockWidget, Shortcut_Manager, 
variable_editor, OctaveTerminal (and TerminalDockWidget!).  What should 
these be?  Does changing the name affect anything else?

I also propose to move all the GUI classes inside the octave namespace.

Any objections?

jwe