Review cmdline module

[scheibel]

• Remove ArgumentParser.
• Provide interface on CommandLineProgram to query the remaining arguments (in case no actions, switches, options or parameters are registered, this would return all arguments)
• Allow for nesting actions (presumably merge action and program or subclass program from action)

[cgcostume]

can you please provide some background on the reasoning and potential benefits of your suggestions.

[scheibel]

The background was an internal discussion with @sbusch42.
We reviewed the currently two existing implementations to parse arguments from the command line (namely ArgumentParser and CommandLineProgram) and decided to merge their implementations.