Add --signature option to remove & filter

[beckyjackson]

See proposal at #483

Currently implemented as --signature <true/false> (-S <true/false>) but this can easily be changed. This works with --trim, for example:

filter --trim false --signature true

Returns all axioms that have at least one target entity in their signature. Alternatively:

filter --trim true --signature true

Returns all axioms that have signatures containing only the entities in the target set.

remove --trim false --signature true

Removes all axioms that have signatures containing only the entities in the target set. Alternatively:

remove --trim true --signature true

Removes all axioms that have at least one target entity in their signature.

The default behavior is --signature false.

[jamesaoverton]

Updated based on discussions from yesterday. As always, it was not as straightforward as I had hoped. I still need to update documentation.

[jamesaoverton]

I think that the new --signature true option is behaving as designed. I've updated almost all the integration tests / examples to use --signature true and they pass. I've updated the docs to reflect the discussion in #483.

I'm going to merge this and make a release. Then we'll see what the next set of problems is.