Implement balance_tracker server API

Add jsonrpc API calls required by new web app:

• find_matching_accounts(partial_account_name) returns an array of all accounts that match against partial_account name. May want to internally limit max amount of names returned by query to something like 2000 with SQL LIMIT option.

• get_balance_for_coin_by_block(account_name, coin_type, start_block, end_block, block_increment) return an array of the balance values for account_name for the required coin_type starting with start_block and incrementing by block increment until last value returned equals or just exceeds end_block. Limit query to returning max of 1000 points by throwing an error if block_increment < (end_block - start_block) / 1000.

• get_balance_for_coin_by_time(account_name, coin_type, start_time, end_time, time_increment) return an array of the balance values for account_name for the required coin_type starting with start_time and incrementing by time_increment until last value returned equals or just exceeds end_time. Limit query to returning max of 1000 points by throwing error if time_increment < (end_time - start_time) / 1000.