isCreator can be removed from API surface

[fulldecent]

This function provides limited utility to the public, since getCreator is already available.

Also, every use of isCreator is from a subclass checking for access control and those subclasses are all Operated.

Recommendation: consider to have Template subclass from Operated and charge isCreator from a public function into an internal modifier.

References:

• Definition: https://github.com/erasureprotocol/erasure-protocol/blob/4a3d98ce023a264a9f3c7ba62ef77a9207bba5fe/contracts/modules/Template.sol#L34

[thegostep]

Keeping Template separate but changing isCreator to internal