Diamond delta magnetic Effector V3

based on a request, and my own personal experiments, i have taken another look at the diamond head design. this design is experimental and untested. This version now includes:
- magnetic arm configuration, matching 45mm width @ the centers (see http://www.thingiverse.com/thing:932914 )
- V3 moves the arm stumps to the top of the effector, thereby giving the arms full clearance from any potential obstacles.
- v3a continues to have the arm mounts at 8 mm from the top, in case the 40mm fan gets in the way. or, if you prefer to have the arms closer to the nozzle.
- refactored the fan mount to a 40mm fan. the 50mm fan mount was obtrusive
- added compatible mounting plate for a BLTouch experimental z-probe that i recently ordered, to give z-probes another chance. others can extend this for their own z-probe models if they so choose.

i won't get to printing one for a few weeks, as i'm rebuilding my delta for the magnetic arms, but I would love to get some feedback on this on how well