Change Twitter label to link, remove Twitter button

[BasThomas]

(I also expected the Twitter link under the author’s name to be a link rather than just a label; the “Follow @…” button is a little confusing, because of course it doesn’t really follow; it just takes you to their page)

https://tryswiftnyc.slack.com/archives/general/p1472998780000011

[BasThomas]

Had a look at this, but the SpeakerTableViewCell used for this is reused in the tableviews. There, it doesn't make sense to have a tappable @name. What do you think, @rnapier?