Make it more dynamic

make it more dynamic, work with lately added li's to the ul. Verifies on every drop who need to have the draggable attr and who doesn't. Support multiple exclude classes. Rewrote the excluding functionality, now it checks in the event callback if it should propagate. Removed the min, because it will be different, and I didn't generated it with closure.

added demo for dynamic loaded content

added a note in the readme for excludes