Add TypeScript support

[belozer]

Because typing is mainstream now

[Shaker-Hamdi]

Yup, I just installed this package and was ready to use it just to find out there are no types for it. So it would be great to add TypeScript support.
I had to go with "react-tabs" just because of this :(

[sashayudaev]

@Shaker-Hamdi why use react-tabs if you could temporarily add your own typings? The library is rather small so it shouldn't be lots of work.

[Shaker-Hamdi]

@sashayudaev When you're in a hurry to meet the deadline, any amount of extra work will hurt you. Plus I'm not that fond of Typescript, to begin with :D. So the idea of typing something that I didn't build myself and figuring out the types gives me anxiety just by thinking about it :D