Merge pull request #15 from AlbertBrand/master

#14 make InResponseTo attribute optional for StatusResponse
InvalidArgumentException at LogoutRequest ->setNotOnOrAfter() #16
 New method in Signature Validator for array of keys #18
New EntitiesDescriptor::getByEntityId #19
AuthnRequest send and Response receive bidnings and url #20
Logging of sent/received messages in Binding #23
Is NameIDPolicy required in AuthnRequest? #21
Missing SignatureMethod element #24
CHMOD lightsaml rwxrwxrx
travis build status icon changed to svg
optionally set signing provider on AbstractRequestBuilder
set signature on created AuthnRequest messages if provider was set