Added Battle.net Provider

I have created a OAuth provider for Battle.net.

I have taken a lot of the code from the other providers which I thought was generic for a standard OAuth authentication.

As default the scope is only wow.profile but there is also sc2.profile. I don't know if both should be default or none.

A Visual Studio version upgrade in the sln file got commited so that can be ignored if possible in the merge later on otherwise I'll have to change that back.

My commit comments is not that good either and I blame me as a first time user of Git and the Windows application for Git.

Hope you'll find this acceptable.