Add ability to track Dollar amounts per user, issue, milestone, and repo

[StephenOTT]

Sometimes the hours or days spent on something is not the factor you want to review your time tracking information on. There are scenarios where you "speak" in dollars :dollar: :heavy_dollar_sign: :moneybag: :money_with_wings: . Being able to say that you have spent $500 on a issue, and only have another $1500 left to spend on a issue, milestone, or repo/project can be a vary valuable metric to have.