C3-Qiskit interface produces results with incompatible state labels about c3

[lazyoracle]

Closed in #59

[lazyoracle]

The fix introduced in #59 misses edge cases. For example 011111 should be flipped to 111110 but that doesn't happen because any leading zeros are automatically removed when converting from binary to hex or int. So 011111 is treated as 11111 and it stays the same. A possible fix would be to delay the conversion to hex until the very last step, before returning the counts in the result data structure. It would then require changes in get_labels() and flip_labels() in c3_backend_utils.py