DATAJPA-506 - Re-enabled query method invocation with wrapper type results.

The custom handling for Blobs applies to strict conversion as it uses the simple method return type to decide whether to trigger a conversion. It now rather uses the returned domain type which automatically unwraps wrapper types like Guava's Optional.

Applied some polishing to the ConversionService setup in JpaQueryExecution to make more obvious that it's only mean to execute very specific conversions.

Added Guava as test dependency and explicit dependency for the Mysema APT plugin as the test scope only would make it invisible for the plugin.