cpp: bin: Amend use of namespaces and relative includes

- Remove unnecessary top-level bin namespace
- Include bin directory in include path
- Don't use relative includes
cpp: showinf: Add copyright and licence boilerplate
cmake: Split up bin and lib subdirectories

This makes additions and changes to components less likely
to cause conflicts.
Merge pull request #1468 from rleigh-dundee/cpp-showinf-fixes

C++: binary build and showinf fixes