Warn on unknown preference setting

[minijackson]

Has this ever happened to you? You configure a service URL in the Phoebus preference settings and it doesn't work. You spent way too much time checking every assumption, such as networking issues, service version mismatch, etc., just to find out you wrote org.phoebus.application.alarm/server = my-server:9092 instead of org.phoebus.applications.alarm/server = my-server:9092.

Ideally, Phoebus should make it clear when it doesn't recognize a preference settings:

• when a preference setting is from an unknown package
• when a preference setting is unknown in that package

I think printing a warning in the logs would be nice, but the logs are a bit crowded. I think it would be good to also have an unmissable visual indication, like a banner, and/or a message in the "About > Preference Settings" tab.

[shroffk]

+1
I think this makes sense.

Will the banner list all the unknown settings?