Expenses

• Add an Expense model with the following properties:
  • amount
  • requested_at
  • requested_by
  • description
  • receipt/invoice pdf
  • ExpenseState model:
    • requested (a manager can request a purchase to be refunded to them) to accepted, rejected, paid
    • accepted (a director can accept a manager's request) to paid
    • paid (when the request has been refunded to the manager)
    • rejected (when a director decides they don't want to pay this)
• Manager UI to request new expense and to review those created by self earlier
• Director UI to list all expenses (filters for state, requester)