Run no formatter by default

[akaihola]

Is your feature request related to a problem? Please describe.
Darker has become a versatile tool for running reformatters, linters and other code inspection/modification tools. For use cases where reformatting with Black isn't desired, and for consistency and symmetry, Black should be enabled only by a configuration / command line option just like other supported tools.

Describe the solution you'd like
If no configuration or command line option for disabling/enabling Black is provided, Black should not be run. In other words, black = false / --no-black OR --format=none should be the default.

Describe alternatives you've considered
Keep Darker as is and add another command line tool which invokes the same code but with different defaults.

Additional context
See

• many-formatters sub-project
• [DESIGN] support different code formatters, allow to skip formatting #304
• Add --black / --no-black options #449