[Feature Request] rules Schema validation

I have not found a similar issue/request

## Summary:

When manually crafting rules files, a json schema would be very helpful to allow validation before placement. The same schema could even be used by opensnitchd to get helpful errors logged.

I've found that the GUI and daemon are inconsistent with showing all the rules or loading all the rules, leading me to think that the rules I'm making might be malformed. Only by enabling DEBUG are more clues available as to the problem - but even then the error/warnings output does not say what the real problem is.

A way to validate the rules would make this experience much better.