Add support for implied language extensions (and let NoImplicitPrelude imply NoDataDeriving)

Based on !55 (merged)

This branch extends the ExtensionCheck to support implied language extensions. Additionally, NoImplicitPrelude now implies NoDataDeriving as suggested in !55 (merged), thereby fixing a bug where declaring data types in a NoImplicitPrelude-enabled module would crash the compiler due to the missing Data class.