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
I'd like to name this function something like `sanitizeSubmissionPayLoad `, as it's pretty coupled to the structure of contrib/interest payloads (due to twittername) and it otherwise suggests that it can be used in a generic way.