move digipot to CurrentCOntrol Module

For those of us not using smoothie board it would be nice if the smoothie board only options were encapsulated in the loadable modules.

Case in point Digipot() is instantiated in Kernel  line 66, but is only ever used in CurrentControl. I would suggest moving it to CurentControl so if CurrentControl is not enabled it never gets created.

Additionally, to save memory, if a module is set to false in the configuration it should delete itself in the on_module_load() otherwise modules like laser and currentcontrol take up valuable heap space.


Thanks.