Bug 20750: Allow logging of arbitrary actions

Bug 20750: Allow logging of arbitrary actions

This patch allows logging of arbitrary actions on request objects. A
chronological summary of these actions can then be displayed when
viewing a request.

This patch also adds logging of request status changes. Additional work
has been done on the BLDSS backend to log requests to the BLDSS request
status check API.

To test:
- Apply patch
- Ensure the Illlog logging preference is turned on
- Create an ILL request and perform actions on it that change it's
status.
- Navigate to the "Manage ILL request" screen
- Click the "Display request log" button
- Observe that a modal opens displaying a summary of the status changes.

Signed-off-by: Niamh Walker <Niamh.Walker-Headon@it-tallaght.ie>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Since this bug now is dependent on Bug 20581, it should be aware of the
custom statuses provided in 20581. This patch enables logging of request
statuses being changed to custom ones. As such the test plan is
modified:

To test:
- Apply patch
- Ensure the Illlog logging preference is turned on
- Ensure you have some custom request statuses defined in the
Authorised Values ILLSTATUS category
- Create an ILL request and perform actions on it that change it's
status.
- Edit the request and change status to a custom one
- Navigate to the "Manage ILL request" screen
- Click the "Display request log" button
- Observe that a modal opens displaying a summary of the status changes.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>