Combine results, apply controlled gates and measure to whole registers

[chriseclectic]

• Fixed measure and control gates to work on registers of qubits.
• Added magic methods to combine Result objects.

Description

• circuit.measure(qr, cr) now will apply measure operations between all qubits in a quantum register and all bits in a classical register. If registers are not the same size it will raise an exception. Eg if both a size 2 it will return qasm measure qr[0]->cr[0]; measure qr[1]->cr[1];
• circuit.cx(qr1, qr2) will apply CNOT gates between each qubit in register qr1 to each qubit in register qr2. If registers are not the same size it will raise an exception. Eg. if both a size 2 it will return qasm cx(qr1[0], qr2[0]); cx(qr1[1], qr2[1]);. The same change was made for cz, cy, ch, crz, cu1, cu3.
• Results may be combined using + and +=. Combining results with + returns a new Result object (using deepcopy), combining with += appends the results from the second result to the first one. For results to be combined they must have the same 'config' value in their qobj.

How Has This Been Tested?

• All previous tests pass
• New unit test test_combine_results has been added to test_quantumprogram.py.
• Test test_run_program was updated to test for measurement between registers.

Types of changes

• Bug fix
• New feature
• Breaking change

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.