meArm Improved Base with Rails

When I printed the meArm, I noticed that the base really was not sturdy enough to support operations.

So I added rails on both sides for structural stability of the base. I fitted the rails with large round feet to which you can attach Micro Suction discs for great stability of the meArm.

While I was at it, I added correct holes and spacers to mount a RPI 3 in the back. Note that to give sufficient clearance for a PWM Controller HAT, increased the length of the screws mounting the rotatio