Introduce event handlers & clean up Entity (#30)

* fix: `ownedBy` typo

* Introduce handle comment created

* Clean up schema & introduce mirror event handler

* Introduce "Collected" event handler

* Add event handlers to subgraph.yaml

* format files

* Fix invalid event handler signatures

* Reintroduce legacy fields in schema

* Add comment to use "rootPubId" instead

* Format code

Co-authored-by: Harpal Jadeja <[email protected]>
Co-authored-by: Nazeeh Vahora <[email protected]>

Author: 3 people