Add gas tracking

[gvladika]

Adds gas tracking actions

yarn run gas:snapshotgenerates the referent snapshot
CI runs yarn run gas:check to test there is any diffs compared to referent values
yarn run gas:report prints out a gas report for contract function

Add a special version of gas benchmarker which prints out the gas diff per function call, for current implementation vs. the deployed version of the code. This reported can be used like this:

❯ yarn run gas:report:benchmark
$ ts-node test/gas-reporter/gasReportChecker.ts
Gas diff compared to referent report:
depositEth: -216 (-0.34%)
withdrawEth_executeTransaction: -21173 (-30.14%)
withdrawToken_executeTransaction: -21379 (-16.42%)

It is also possible to run benchmarker against any referent code.
First generate referent report by running:
yarn run gas:report:gen-referent - this will store output to .referentGasReport
Then checkout the other version of code and run benchmark action:
yarn run gas:report:benchmark - since there is existing .referentGasReport, that will be used as referent report instead of the production code one