Bug 8367: (QA follow-up) Improve display when value not set for rule

Bug 8367: (QA follow-up) Improve display when value not set for rule

When a rule is not set for a speficic line, the value in the syspref
will be used. This should be made clear in the interface.

To test:
1 - Add a new rule for a specific item type
2 - Do not fill the 'Hold pickup period'
3 - Confirm that the rule defaults to the system preference
4 - Hover on 'Default' in the circ rules under 'Hold pickup period'
5 - Confirm the text is readable

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kelly <kelly@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kelly <kelly@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>