fix(rpc-calls): Calculate gas for empty accounts

[breathx]

Bug description

Sometimes it happened that user couldn't calculate if his balance is zero. Especially it caused vouchers consumers.

This was happening despite the fact that the balance is mocked to suit the requirements of the call.

Bug mechanic

In order to increase accuracy of required gas measurement, the measurement is done twice:

• First time we run message with maximum gas limit, receiving some minimal limit
• Second time we run message with minimal limit from previous step to receive even smaller gas amount in case of gas-dependency of the message execution.

It happened that minimal limit (in gas) can has value equivalent less than existential deposit, so our balance mocking using deposit_creating occurred no-op.

Bug fix

Always add up existential deposit in calculate gas rpc call balance mock.

NOTE: Minor refactoring is done as well

[shamilsan]

👍