Improvements on Schematics Design

[jgvictores]

From https://github.com/roboticslab-uc3m/Dextra/issues/5#issuecomment-502228968

• Reverse the Pololu connector pinout, i.e. bring the ground pin back to the left side (so that wires need not to be flipped on their way from the board to the Pololus).
• There are several screw holes, we just need two (top-left and bottom-right). Removing them would leave more room for the CAN transceiver (https://github.com/roboticslab-uc3m/Dextra/issues/2) and the DC/DC converter (https://github.com/roboticslab-uc3m/Dextra/issues/3).