Ability to Manually Edit Total

user story: as a user creating/editing a proposal, I would like the ability to manually adjust the total total, so that I can raise/lower the cost easily without needing to apply a discount or adjust individual prices on line items or substrate calculations.

Example: as a user creating/editing a proposal with a total balance of $5000.00, I would like the ability to change that number to $4999.00 without having to apply a $1 discount.