New rigid header for FT5

** 20170228 : Attention -- Possible issue when in a hot environment **
I ran in a tolerance issue when printing ABS. The top part of the printer was around 50°C and the thermal expansion caused step skipping due to grinding between the stepper motor and the 2020-profile. I've added some extra room (2mm) between the stepper and the 2020-profile with a new front and back plate.
Unless you only print PLA, I strongly recommend to use files **FrontV2.STL** and **BackV2.STL** !!
Tested and works nicely now. See last picture for the added room between profile and stepper.

I made also a new **TOPV2.STL** for the cablechain mount. This one has, like the bottom piece, complete support for the bolts.

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A redesigned header for the FT5. Push once to the tip of your hotend to the back/front to see what I mean with rigidity.
Extra support for the bolts, extra ribs on front- and backside, higher bottom- and top part give extra rigidity to the header. Absolutely no play in Y-