Add a Develop menu with Nu/Vico development utilities.

This menu is currently toggleable like the Safari Develop menu. It contains
three items:
 - `Reload Bundle`: reloads the working directory as a bundle.
 - `Toggle Console`: shows/hides the console (loads it if it isn't loaded yet).
 - `Evaluate File/Selection`: evals either the current file or the current
   selection (when there is one).

To support the first two items, two ex commands are also added:
 - `:reloadbundle [path]`: with no path, reloads the working directory as a
   bundle. Given a path, attempts to load that path as a bundle directory.
 - `:console`: shows/hides the console (loads it if it isn't loaded yet).

This allows these same commands to be bound to keyboard shortcuts if desired.