Style: apply cpplint to headers and source in core lib

[srmainwaring]

This PR adds a cpplint workflow and includes changes needed for the code in the core library to run clean.

Details

The cpplint workflow is:

.github/workflows/cpplint.yml

with a configuration file:

./CPPLINT.cfg

We set the following filters:

filter=-whitespace/braces,-runtime/references,-build/c++11,+build/c++14,-build/include_subdir

• -whitespace/braces: allow opening curly braces on following line after classes, conditionals etc.
• -runtime/references: allow pass-by-reference modifications (Google insists on using pointers).
• -build/c++11,+build/c++14: allow #include
• -build/include_subdir: unclear how to address this for headers in the src folder we don't want to export.

The CI covers the core libraries - the remaining files will be added to the coverage in follow up PRs.

There are a lot of changes in many files, however it is mostly formatting to comply with the linter.

• Rearranging includes
• Adjusting indentation (i.e. no-indent inside namespace).
• Stripping the per-method public, private declarations (i.e. not Gazebo style)
• 80 char line limits
• Removing trailing whitespace