Allow commands to accept arbitrary panes to operate on
Fix typo when fetching verbosity preference
Address several large items:

 - Organize code in a more logical/readable order
 - Give panes a reference to their editor
 - Overhaul how the command bar is implemented. There can now be one
   command bar for each open pane, focus/blur behaviour is more intuitive,
   and functionality was taken out of the Editor class.
 - Improvement on how panes track their focus state
 - Implement more robust object inheritence using Object.create()
 - Doc updates and bugfixes