feat(generator): Add option to disable code formatting

Add option to disable the automatic removal of unused imports from generated files. This is very annoying behaviour with hidden libraries as in that case it is really nice to already give students the imports they can use, even if the solution template does not use them.

Disabeling this behaviour would also keep the decorator imports that should not be visible at all. autolake does not normally support only removing certain unused imports, but it can be accomplished by changing a static constant. For future proving the old state is restored, but this is not needed right now as the entire generator switches to this behaviour and not a single file.