DATACMNS-509 - Fixed non-NullableWrapper conversion.

In case the repository method execution returns a collection that needs to be converted into a different collection (e.g. List -> Set) we erroneously ran into a NullableWrapper conversion. This was due to the fact that we only used the raw method return type, which caused the ObjectToCollectionConverter to kick in (as the target type's component type falls back to Object if we use raw types).

We're now using Spring's MethodParameter abstraction to create a TypeDescriptor for the method's return type which fully supports generics, so that the conversion check for NullableWrapper -> target type does not match the ObjectToCollectionWrapper.

Prepared the QueryExecutionConverters to be able to support recursive type conversion once we move to Spring 4 as TypeDescriptor exposes the ResolvedType as of this version so that we can inspect the type parameter of the wrapper type to invoke a nested conversion (e.g. Integer -> Optional<String> requires NullableWrapperTo(Guava|Jdk)OptionalConverter being invoked and in turn recursively convert the Integer to String).
DATACMNS-508 - Re-enable Querydsl profile for Travis build.