Twitter support!

This allows to submit your twitter profile to submissions and interests (82778f3)

We also got a tweet-about button after the creation of a talk/interest. It is cookie based like votes. (fc78203
)

this needs #34 and #33 (hapi updates) and #37 (XSS, filtering) merged before, they are included in this optimistic branch
What do you think about adding:
`expect(sanitized.twittername).to.equal('robinson_k');`

So we can be sure that `twittername` wasn't changed into some gibberish. :)