* Change --gas=0 semantic and introduce --gas=simulate
Make --gas flag accept a conventional "simulate" string value in addition
to integers. Passing --gas=simulate would trigger the tx simulation and
set the gas according to the gas estimate returned by the simulation.
Any other integer value passed to --gas would be interpreted as-is and
and set as gas wanted value.
Closes: #2300
* Add test cases with gas=0
* ACK suggestion from @alexanderbez
* s/GasFlagSimulateString/GasFlagSimulate/
* Drop TODO comment on Gas type
* Enrich TODO with ref
fb0cc0b078