Core API: avoid duplicates in undo/redo preview
Copypaste: refactoring + return all pasted ids
Organism: carry rules on event
Organism: add to API
Links: change API
Links: do not always signal rules event when upserting
Links: signal new events
wx Gui: introduce item properties and icons

Addresses #231
wx Scheduler: introduce item icon

Addresses #231
wx Links: introduce item icon

Addresses #231