[5.x] Slight adjustments to the search index table

[daun]

Spent a lot of time in the search index screen recently and found a few little spots to optimize :)

• Make sure the icons aren't squished when the other columns grow
• Add an icon for unknown/custom drivers
• Add an icon for the Loupe search engine
• Make sure everything is top-aligned

Drive-by changes

• Setting a fallback unknown/custom driver icon required updating the svg helper to optionally pass in a fallback icon in case the requested one doesn't exist. Might be useful in other future use case as well?

Before

After