Added possible gas estimation for participant registration

[Flash-Git]

I haven't built the project so this addition is untested.

Code based on my own experience with web3 v1.0 and the docs.

If you are not using 1.0 then it looks to be slightly different.

v0.2 contract.myMethod.estimateGas() https://github.com/ethereum/wiki/wiki/JavaScript-API#web3ethdefaultblock v1.0 myContract.methods.myMethod([param1[, param2[, ...]]]).estimateGas(options[, callback]) https://web3js.readthedocs.io/en/1.0/web3-eth-contract.html?#contract-estimategas

Hopefully this is helpful.

EDIT: To be clear, this probably isn't functional as is.