cpp: bioformats: PixelProperties supports pixel types of different endianness

Add support for native, big and little endian pixel types using `Boost.Endian`.

Testing: `cpp/test/ome-bioformats/pixelproperties` unit test in place; check if job is green.

https://github.com/rleigh-dundee/bioformats/compare/cpp-pixelprop-endian...cpp-pixeldata?expand=1 is work in progress on using these types in a variant multiarray pixel buffer.

Travis needs kicking after timeouts.