TN: Choose balance when creating an account using server

[relativityboy]

As a developer I want to be able to create accounts with a decent (and specifiable) balance so that I can test my wallet/app with accounts that have both high and low balances.

AC

• account_create supports specifying a balance
• web interface for account creation supports specifying a balance.
• there are configurable constraints within tinman to restrict the maximum createable balance to something that will allow the chain to continue functioning.