Take more advantage of namespaces / use statements (#1139)

lib/SimpleSAML/Auth/AuthenticationFactory.php

lib/SimpleSAML/Auth/Default.php

lib/SimpleSAML/Auth/ProcessingChain.php

lib/SimpleSAML/Auth/Simple.php

lib/SimpleSAML/Auth/Source.php

lib/SimpleSAML/Auth/State.php

lib/SimpleSAML/Auth/TimeLimitedToken.php

lib/SimpleSAML/Bindings/Shib13/Artifact.php

lib/SimpleSAML/Bindings/Shib13/HTTPPost.php

lib/SimpleSAML/Configuration.php

lib/SimpleSAML/Database.php

lib/SimpleSAML/Error/Assertion.php

lib/SimpleSAML/Error/CriticalConfigurationError.php

lib/SimpleSAML/Error/Error.php

lib/SimpleSAML/Error/ErrorCodes.php

lib/SimpleSAML/Error/Exception.php

lib/SimpleSAML/Error/NotFound.php

lib/SimpleSAML/HTTP/Router.php

lib/SimpleSAML/IdP.php

lib/SimpleSAML/IdP/IFrameLogoutHandler.php