When linking an item to a virtual collection via KAddressBook, canPaste check
fails because it's not aware of the context (i.e. action is Link, not Copy)
and checks only for CanCreateItem (which is not correct if we're linking).

This patch provides Qt::DropAction action parameter to canPaste method so
it is aware of action, and check for correct permissions based on that

1. Link an item via KAddressBook using Drag'n'Drop to some virtual collection

(e.g. Google Contacts Resource)

2. The item gets actually linked, instead of silently ignoring