Reduce 2x buffer for gas limit

[arhag]

Depends on eosnetworkfoundation/eos-evm-node#50 and eosnetworkfoundation/eos-evm-contract#663.

Right now the frontend sets the gas limit to twice the estimated gas. This is to workaround issues in the EOS EVM Node which underestimates the appropriate gas estimate (eosnetworkfoundation/eos-evm-node#50) and in the EOS EVM Contract which requires a higher gas limit than should actually be necessary (eosnetworkfoundation/eos-evm-contract#663).

Once those two issues are resolved, the frontend can be updated to reduce the buffer it uses to 10%. Some buffer is still desired because evolving state could cause the contract execution to go down slightly different code paths which end up consuming a little more gas.