Implement #673

Conflicts:
	builds/appchan-x.user.js
	builds/crx/script.js
	src/General/Config.coffee
	src/Images/Gallery.coffee
Gallery improvements: now loops.

Conflicts:
	builds/appchan-x.user.js
	builds/crx/script.js
	src/Images/Gallery.coffee
make slideshow mode loop; update gallery menu