Come up with deterministic strategy for gas calculation

[swift1337]

In TON a smart contract might consume gas for its invocation.

We need to make sure that technically and economically in any circumstance :

• Deposits / withdrawals / admin commands have enough gas
• Gas consumption doesn't affect locked funds
• Huge cross-chain payloads don't affect locked funds
• Gateway can't run out of gas (also take into account storage costs)
• Gas calculation is deterministic up to certain ceiling

Also, should we add some getter that returns a ballpark estimations for potential deposit / deposit_and_call? This might be useful on frontend for showing approximate tx costs