fade long tag names - refs diaspora/diaspora#3899

I implemented the fade for the tags as was suggested by @asphxia

I patterned the css after this jsfiddle I found:
http://jsfiddle.net/x4gSG/1/

There are no tests included, but it's only CSS changes, so I assume that's ok. I tested it myself in Chrome and Firefox and it appears to work.