[Feature] Add an option to delete unused files

[ArnaudB88]

In our company, we use your generator for many years now with many developers. Over the years, we added some features so it works better with our solutions. As a sign of appreciation, I want to suggest some features because I think it will help some other developers as well.

Feature description:

Add an option to delete files which don't have a matching database table

Feature motivation & example usage:

When a table is removed or renamed, the efg tool currently doesn't remove the old generated files. The developer should cleanup his files manually, which can be forgotten.

The option is a boolean, true enables the feature.

YAML usage:

data:
  entity:
    deleteUnusedFiles: true
  mapping:
    deleteUnusedFiles: true

Please review the feature request and evaluate if you think this is an addition to your repo.
(pull request will be added)

Thanks