LinkedIn Support Oauth2

Also made a linkedIn Support for Oauth2, this way seemed a bit more simple ;)
Would also be nice if we could add a Twitter version only problem is that it is Oauth not Oauth2, but if you want I could build that in. It would be nice to have so that could also be used in the thinktecture identity provider. if this or that other version gets merged, I can also add the new providers to Thinktecture and make a pull request for that if ya want.