Skip kendo-ui-core components that aren't available. #359

Currently angular-kendo assumes that the entire kendo-ui-core library is being loaded. For those of of us using custom builds to select only the components we need, angular-kendo fails on line 519 because the class name passed into it doesn't exist.

This change short-circuits defadvice() so that it doesn't bother trying to hook up kendo-ui-core components that aren't available.