Refactor Subsystem Factories to Have Base Class

[stulewin]

The loading of the implementation class can be done similar to the way Command loading is done now, and put in a base class to minimize the amount of code (and copy and paste errors).

/** Name of our robot implementation */
protected static final String robotImplName;

static {
    PKProperties props = PropertiesManager.getInstance().getProperties(Robot.name);
    robotImplName = props.getString(Robot.implementation);
}