LP#1641708 Work log avoid storing unneeded data

LP#1641708 Work log avoid storing unneeded data

Avoid storing full transaction data with each work log entry.  Only
store data need for work log display and actions.

Includes the addition of a new field (entry.hold_id) for hold requests
so that the value does not have live in the large data blob.

To test:

1. Peform checkouts, holds placements,  and other log-tracked actions
   in the client.
2. Open Administration -> Workstation -> Stored Preferences and see
   values for key "eg.patron_log".  Values added after the patch will only
   contain ~8 keys with string values, no large nested objects.
3. Open Administration -> Local Administration -> Work Log and confirm
   recent log-tracked actions are all represented in the grid.

Signed-off-by: Bill Erickson <berickxx@gmail.com>