Dryrun cost

[tzaffi]

Upgrade the treatment of Dry Run Cost + Handle dryrun_accounts

This continues the almost ready to merge #31

Original PR Description

For certain use cases, it's necessary to set the balance of the app account to some nonzero value. One example is testing inner app calls. This PR allows the users to set balances for accounts and updates the existing dryrun cost field (which is now deprecated) and adds support for the new cost fields BudgetAdded and BudgetConsumed.

Testing: Unit tests.

[michaeldiamant]

@tzaffi Thanks for picking up the effort here - Looks good to me. Consider my remarks optional.