Improved Servo Bracket

This version has the following changes:-

Made the .scad file more modular and improved the parameterisation
* Added a hole and various slots for more mounting options
* Rounded the corners and made the default size thinner to reduce printing costs
* Added braces for extra strength
* Added hooks to suspend the cable that connects to the servo

NOTE
I haven't been able to get this to print on our Makerbot yet