Add support for modal toggling and tracking all active modal instances

[swg]

This pull requests adds support for closing all active modal instances (if no target modal is passed) and enables "toggling" of modals with onShow. Previously this behavior was buggy, and would only ref the last activeModal for closing.

[auriel-klasovksy]

This is perfect. Thank you very much, hope this gets pulled.

[kauaicreative]

Watching for this