C++: binary build and showinf fixes

- Clean up use of namespaces and includes
- Add copyright/licence boilerplate

Note use this diff: https://github.com/openmicroscopy/bioformats/pull/1468/files?w=1 to filter out the whitespace changes.

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Testing:

- build should be green (will fail if includes and namespaces are incorrect)
- showinf should continue to work (run `./bf cpp/bin/showinf/showinf --help` to verify)