Fix bugs (minor one & major one)

Details:
- fix wrongly computed bit error rates (number of errors was
  divided by incorrectly caclculated number of bits, hence the
  error rate was underestimated)
- fix demodulation - index of demodulated symbol was used as a,
  result of demodulation instead of label (BitWord) that supposed
  to be used for that, as a result any different mapinng of bit words
  to constellation symbols couldn't be used.