Cleanup output streams in GridKit core code

[nkoukpaizan]

Description

This updates most of the output streams in the GridKit folder to use the Logger instead of std::cout/std::cerr.
Closes #512

Proposed changes

• Introduced GRIDKIT_ENABLE_DEVELOPER_MODE, that currently increases the default verbosity. I envision using this for other purposes than verbosity levels.
• Introduced Logger::raiseVerbosity to prevent unintentionally lowering verbosity in applications and examples.
• Replaced the std::cout/std::cerr calls I think are worth keeping.
• Replaced most std::endl with "\n".
• Removed commented out std::cout/std::cerr that only reported "tracing/debugging" information.

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• [N/A] There are unit tests for the new code.
• [N/A] The new code is documented.
• The feature branch is rebased with respect to the target branch.
• The CHANGELOG.md has been updated to reflect the changes. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

We can either squeeze this in before #596 or defer to after the release.

[lukelowry]

Very helpful thank you for the developer mode flag

[pelesh]

Thanks for the much needed cleanup!

What is the difference between setVerbosity and raiseVerbosity? It is not clear to me why we can't use setVerbosity only.

[pelesh]

CC @Steven-Roberts @alexander-novo

[nkoukpaizan]

Thanks for the much needed cleanup!

What is the difference between setVerbosity and raiseVerbosity? It is not clear to me why we can't use setVerbosity only.

The difference is asserting that the target verbosity is higher than the previous one. We could use setVerbosity only, but that puts the burden on the caller to check.