Add support for manual acq fund adjustments / journal entries

[Galen Charlton]

It could be useful to have a mechanism for adding fund debit and credit entries for the purpose of adjusting fund balances for reasons other than purchase order and invoice activity.

Such entries might be called fund adjustments or journal entries and should have at least the following attributes:

- a required field to describe the purchase of the adjustment
- who made the adjustment
- creation date
- affected fund
- amount
- permissions to control who can make and revise such adjustments

This could be worked around by using fund allocations, fund transfers to dummy funds, or direct charges on fake invoices, but an explicit adjustment mechanism would be cleaner.