Added Model UpdateBalanceHistory to track update_balance

Added update_balance_history_id col to
- UserPayment
- UserDept
- UserBalance
Fixed some tests related to UpdateBalanceHistory
Fixed update_balances method to accept user_id

Added and fixed tests relating to UpdateBalanceHistory
Fixed "process" Expense method to accept user_id

This method links to update_balances method from UserBalance which
requires user_id
Added reverse relationships to UpdateBalanceHistory
Updated TODO.txt