This PR resolves issue #244. It looks like the only issue was that converting a constant to a state space object was creating an extra state and this state had to then be removed. By creating a state space system with no internal state (A = [[]] instead of A=[[0]]), this action is no longer required to get sensible results from block diagram algebra functions.

The PR makes that change and also changes the default value of statesp.remove_useless_states to False.