Adds the ClientCertificate to the Request

For Hosting.Aspnet, Hosting.Wcf and Hosting.Owin. I've also done a
pull-req to https://github.com/prabirshrestha/simple-owin/ to make that
send the Certificate on in the ssl.ClientCertificate env variable.
In tests the ClientCertificate property is null.

IIS fills this with an empty object. Thats why I check for .Length == 0.
Code clean up. And added the certificate to the

OWIN env in the owin demo. So I can refer to that in the documentation.
Bit more Stylecop OCD.
Also adds the ClientCertificate in Hosting.Self
Changes according to @thecodejunkie

WCF Claimset doesn't assume [0] is the X509CertificateClaimset anymore.
And the certifcate variable name is now the same in every host.
Typo and whitespace.
Merge pull request #1033 from albertjan/clientcertificate

Adds the ClientCertificate to the Request