Feature: better visibilty of palette catalogues

[knolleary]

The palette manager can be configured with multiple catalogues of nodes. It currently defaults to the catalog provided by flows.nodered.org.

If a custom catalog is provided, its contents are included in the search results within the palette manager - but there's no way of knowing which catalog a result comes from, or to be able to restrict search results to a particular catalogue.

This issue is to improve the UX of the palette manager when multiple catalogues are configured.

Ideas to look at:

• Allow search results to be filtered by catalogue
• Include catalogue information against individual search results
• Look at how a catalogue with basic auth applied could be handled

[MarianRaphael]

Feedback from veloce-cloud on FlowFuse/flowfuse#217

"It will be nice to filter either node catalog by Open Source license type as well and date last updated."