Bug 827133 - Support unavailable builds in new Sandstone Firefox languages page.

https://bugzilla.mozilla.org/show_bug.cgi?id=827133

Added support for unavailable builds for a platform in a given locale in all.html. Created new unavailable CSS style for them (display: none in 320px screens), and added mockup icon.

Added macro build_link to all.html to streamline platform column creation.