Ensure EOSJS supports BigInts

[ericpassmore]

Review code for numbers passed as parameters. Look to support BigInts. From issue originally reported in https://github.com/AntelopeIO/leap/issues/579

• Review all functions calls with numeric params in EOSJS for BigInt support.
  • safest thing is to make all numbers BigInts, as numeric operations my result in BigInt
• Consider specialized functions to wrap BigInt -> Numeric conversion
  • safely convert to unsigned
  • customized exception when number can not be converted