Gallery items should implement Invokable so the class can be
invoked from the New Gallery. Gallery elements should be registered
declaratively and all information necessary to display the item
defined in the extension.xml. The item's name must be the
fully-qualified name of an Invokable class.
context - The context of the wizard. All parameters required
by the wizard must be set on the context. The wizard may also
return values to the caller by setting them into the Context for
the caller to retrieve.
Returns:
true if the invocation was successful, false
if it failed or was canceled