Merge of qcircuit_measurement branch to allow simple measurements. 

The changes in this PR make a "fake" measurement operators Mx and Mz. These does not implement real quantum measurement, is specially flagged with a "measurement" property so that the circuitplot routines can identify the qubits after this operation as having been measured. The circuitplot utilities then double the qubit wires after this gate, as well as the controlled lines hanging off the qubit wires.