Add twitter share button

[bmwwoo]

No description provided.

[ericthewry]

Well want to incorporate this into #73

Not necessary now, but well want to do that in the future.

LGTM

[ericthewry]

Actually, wait, I take that back. We should call this TwitterShareService or something in case we want to include other social media. Then ShareGameService would manage all of the social media.

I think we should keep ShareGameService and then TwitterShareService managed by it. Then we'll also have FacebookShareService and TumblrShareService or whatever else (not for this PR), and ShareGameService will do whatever initializing and location management needs doing.

[ericthewry]

LGTM 🚢