Make SampleMvcApplication point to local StubIdp

Pro: This makes it easier to get the sample application started
Con: It is harder to understand the config file when the host name is
not sensible
Merge pull request #63 from albinsunnanbo/MakeSampleApplicationPointToLocalIdpStub

Make SampleMvcApplication point to local StubIdp
- This makes sense for now, when the stubidp follows the ACS in the AuthnRequest the sample app should point to http://stubidp.kentor.se instead.
Merge branch 'master' of https://github.com/KentorIT/authservices
Check for incorrect transforms in XML signature.
- The SAML2 Core spec section 5.4.4 states what transforms are allowed, check that no others are used.
Fixes after code review of pull request.
- Added comment to Saml2Response_Validate_FalseOnIncorrectTransformsInSignature making clear the wrong transform is used.
- Now using built in constants for XML Dsig URNs.
- Refactored Saml2Response.CheckSignature to make code more readable.
Merge pull request #64 from AndersAbel/55RejectWrongTransforms

Check for incorrect transforms in XML signature.
Merge branch 'master' of https://github.com/KentorIT/authservices