go.talks: handle scrolling events to navigate slides
go.talks: handle scrolling events to navigate slides

R=r, adg
CC=golang-dev
https://codereview.appspot.com/12271043

webfd/go-zh.talks,d0f/go-zh.talks,bryanxu/go-zh.talks,webfd/go-zh.talks,webfd/go-zh.talks,d0f/go-zh.talks,webfd/go-zh.talks,d0f/go-zh.talks,webfd/go-zh.talks,d0f/go-zh.talks,bryanxu/go-zh.talks,d0f/go-zh.talks,d0f/go-zh.talks,bryanxu/go-zh.talks,webfd/go-zh.talks,bryanxu/go-zh.talks,bryanxu/go-zh.talks,bryanxu/go-zh.talks