Alternate basic damage

[NagBoard]

It would be great to be able to add new damage schemes like we can do with attributes. Main purpose right now is calculating FDG damage automatically, but can be used for other rules. It would probably result in refactoring damage schemes though, because they would be covered under this system and all previous work will become obsolete.

Additional solution might be just creating checkbox in sheet settings to display FDG damage, that would be easier and would not require rewriting the whole damage module.