Improved deployment pricing

[miloszm]

This PR improved deployment pricing in such a way that the cost of deployment should not be negligible to the user.
The deployment charging behaviour is controlled by the following configuration items:

gas_per_deploy_byte
min_deployment_gas_price

Transaction containing deployment will be discarded if the minimum transaction gas price is insufficient.
The defaults are set as follows:

const DEFAULT_GAS_PER_DEPLOY_BYTE: u64 = 100;
const DEFAULT_MIN_DEPLOYMENT_GAS_PRICE: u64 = 2000;

Current defaults should enforce reasonable deployment costs in the real world.

Implements #2207

[ureeves]

LGTM

[herr-seppia]

LGTM