LP#1175293 Use filtered fund dropdown in funding source interface

LP#1175293 Use filtered fund dropdown in funding source interface

The exising interface for allocating to funds from a funding source
view lists all funds by code only.  Since many (most?) orgs reuse
fund codes year to year, you eventually end up with a bunch of
dupes you cannot tell apart.

Let's "borrow" an AutoFieldWidget to do the heavy lifting of creating
a filtered list of active funds, and include the year for further
user validation.

This is inspired by a few other fund dropdowns, but may not be the
best overall solution.

Signed-off-by: Dan Wells <dbw2@calvin.edu>