allow only valid cases for livenet

Valid m/n pairs are:
# m, n, maxScriptSigSize
[ [ 1, 1, 113 ],
  [ 1, 2, 147 ],
  [ 2, 2, 221 ],
  [ 1, 3, 182 ],
  [ 2, 3, 255 ],
  [ 3, 3, 329 ],
  [ 1, 4, 216 ],
  [ 2, 4, 290 ],
  [ 3, 4, 363 ],
  [ 4, 4, 436 ],
  [ 1, 5, 250 ],
  [ 2, 5, 324 ],
  [ 3, 5, 398 ],
  [ 4, 5, 470 ],
  [ 1, 6, 284 ],
  [ 2, 6, 358 ],
  [ 3, 6, 431 ],
  [ 1, 7, 318 ],
  [ 2, 7, 392 ],
  [ 3, 7, 466 ],
  [ 1, 8, 353 ],
  [ 2, 8, 427 ],
  [ 1, 9, 387 ],
  [ 2, 9, 461 ],
  [ 1, 10, 421 ],
  [ 2, 10, 495 ],
  [ 1, 11, 455 ],
  [ 1, 12, 489 ] ]

fixes https://github.com/bitpay/copay/issues/212