Expose nitf::BandInfo to python

[ianrcooke]

The NITF BandInfo portion of the Image Segment Subheader is not exposed in the six sicd Python bindings and thus values in the BandInfo can't be accessed.

I'm not sure what six-library's stance is regarding exposure of NITF elements to Python, but it would be convenient to access all NITF data via one API rather than having to try to glue together different solutions, e..g opening the file both in nitro's and six-library's python bindings.

This is fairly straightforward to expose simply by %include nitf/BandInfo.hpp; and then dealing with LookupTable's lack of a default constructor, either by defining one in the .i file, or ignoring the offending method via %ignore nitf::BandInfo::getLookupTable;

See also #352 regarding access to BandInfo in the first place.