Missing null checks

[eztierney]

In several places in the code, addresses are passed as parameters to functions. In many of these instances, the functions do not validate that the passed address is not the null address 0. In the Controller contract, this happens in functions configureController (which only checks _worker) and removeController.

In the MintController contract, on the other hand, it might be expected that the constructor sets the minterManager variable to 0, but the setMinterManager function does not prevent setting it to 0.