Update look of Smart Search filter gallery

[ziggabyte]

Description

This PR updates the look of the Smart Search filter gallery, by making it more like the column gallery used in lists.

Screenshots

Changes

• Adds sidebar with index of all categories, that scroll into view when clicked.
• Updates the look of the cards, and gives each a CSS "image" that is actually a complex gradient.
• Changes the names of the categories, and gives them descriptions
• Adds one new category, Cross referencing, and splits the previous "campaign participation" category into Events and Tasks.

Notes to reviewer

• We have not updated the "header" part, so it does not fit in visually at all and we are aware of that heh

[richardolsson]

Great work on this! I'm suggesting some minor changes below, and then there is a merge conflict, and the need to also add email filters now that they've been merged to main. Can you sort that out and then lets merge? 😊

[richardolsson]

This looks good to me, and ready to merge! 💯

I will merge it right away in order to discover any merge conflicts that may arise with #2008.