Levelable Greg-Wade-Jonas-Misan extruder support for Prusa i3

Levelable Support for classical extruders. Thanks to the possibility to modify height it could be adapted to any hot-end (independently of its lenght). It has been tested with the Buddasch Nozzle and the J-Head

It works perfectly with:
* http://www.thingiverse.com/thing:32953
* http://www.thingiverse.com/thing:18379
* http://www.thingiverse.com/thing:65939