R1:3349c3be17c7

Fix call to non-existing newWorkCommands() in NuanceItemType

Summary:
rPe1b8532e2478395bd1f36baecb998adeef5bea3d introduced an implementation of `newWorkCommands()` in the child class `NuanceFormItemType` which is called in parent `NuanceItemType::buildWorkCommands()` without being defined in that parent class.
Thus define `newWorkCommands()` as an abstract class in parent class `NuanceItemType` and add an implementation returning null in the other child class `NuanceGitHubEventItemType` to make static…