Inconsistency: SAML helper transforms binary guid to upper-case

[JakubDolba]

\SilverStripe\SAML\Helpers\SAMLHelper::binToStrGuid
is converting GUID to uppercase after binary conversion

• but this applies only for option expect_binary_nameid = true
• other options will use value from SAML as it was received (lowercase most likely)

there are related issues with that: #17 and #20
also there is pull request to normalize GUID before usage but there is still inconsistency in behavior ( #18 -> solve #17 )

expectation:
consistent behavior (one of upper or lower case guid) should be default for all options