Fix is and is_not vertex unwrap 

Added a few spec lines for testing is and is_not operations with vertex, and added a way to unwrap every object that answer to :element in order to get a proper blueprint graph over there. Like this every non basic type, so everything coming from a Pacer wrapper will be unpack before being send to the ObjectFilterPipe.

This fix https://github.com/pangloss/pacer/issues/40

Comments, reviews and suggestions are of course accepted ;-)

- purbon