Fix tapping on usernames, spoilers, images, etc.

I hadn't realized that FastClick synthesizes click events where iOS by default
does not. Bringing back Zepto's touch module adds a zero-delay "tap" event. The
alternative was to add empty "onclick" attributes to anything we wanted to
click, but I like fewer delays.
Fix smileys and other leeched images in previews.

Need quotes around that attribute selector or it matches anything starting with
"http"!
Hide (nonfunctional) action button in post preview.
Don't follow links in post preview.