frontend in Go

Hello Andrew,

you said at dotGo that the JavaScript part is kind of diminishing the fun of working on sigourney and that GopherJS might be a solution to that. I took you by your word and wrote a Go version of the frontend. I applied some optimisations and the protocol is now shared between frontend and backend. There is still a lot of room for improvements, e.g. some libraries by the GopherJS community may be used to wrap the JavaScript calls in a type-safe fashion. I hope you like it!

Cheers,
Richard