Add visibility options for image tabstrip

I debated the merit of displaying these options to the user, and
eventually decided it was worth it.  Other toolbars can be selectively
displayed/hidden so it seems unnatural to omit the image tabstrip
(especially for those who seek a truly minimal interface).  Also, I'm
one of those weirdos who likes tabs always visible in my web browser,
even when only a single page is open, so I should extend the same option
to PD users.

Per PD convention, these options are exposed directly in the Window
menu, not in the Options dialog.
Fix «/» detection in Google Translate module

Thanks to Zhu JY for discovering this
Add alignment options for image tabstrip

Includes syncing with preferences file, and full communication with the
window manager.

Now all that's left to do is add code to the tabstrip to redraw itself
(and modify all input behavior) if it's in a vertical alignment.