Fixed-width grids & fix to non-modal picker panes

Sorry about the dual-featured, poorly-timed pull req but here are two straightforward enhancements.

- Fixed-width grids adds a new toggle which allows you to easily make your grid items not stretch to fill the line.  (I'm building an imitation file system view; I don't want the icons to spread out as the window is resized.)

- Currently, even if you set your picker panes to non-modal, they will still disappear if you click the modal background, which may be showing from a different picker pane.  This can result in things like unexpected and jarring partial dismissal.  This one-line fix prevents that behavior.