Add icons to multi-valued custom groups and display on contact tab

[colemanw]

Overview

Allows selecting an icon for custom tabs on the contact summary screen.

Before

Custom tabs were always "fa-gear"

After

Now you can pick an icon for custom fields displaying as "Tab" or "Tab with Table" on the contact summary screen.

[civibot]

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[MegaphoneJon]

This is already possible with Contact Summary Layout, is it not?

[colemanw]

@MegaphoneJon yes that extension can edit icons on the tabs.

However, the reason I want to add this to core is also for the benefit of the new Search Builder UI.

I just did another PR to add translated titles and icons to core entities. These get exposed, via APIv4, to the Search UI.

Multi-record custom field sets are also treated as "Entities" by APIv4 and the search UI, so this gets them on par with those features of core entities.

[colemanw]

retest this please