Fixed what appears to be a bug in MappingProcessor. 

It appeared that the mapId for objects within collections was not being passed to the
call to mapToDestObject which results in incorrect mapping. For example
when specifying TypeMappingOptions.mapNull(false) nulls were still mapped.

Have added a unit test DeepMappingWithMapIdTest which fails with the unpatched code and passes with
the patch applied.

I have logged the issue Issue #135.