Tronxy X3 or X3A Bed Upgrade Remix

2018/03/21 Changelog for remix:

- Resized bed support to fit the acrylic bed with "X3" on it.
- Changed clamps on bed support to use nut and bolts.
- Made new endstop and rod holder.
- Rod holders only require 1 screw each.
- Resized opening for nut to fit easier in the tensioner and made a tiny slice.
- Made a spacer for pulley to raise it to the perfect level.

Things needed are:
- 400X8mm Linear Rods X2
- Nema 17 Stepper Motor Steel Bracket
- Original M2 Machine Screws and Nuts f