Improve most visited page

Various fixes to make the most visited page nicer, especially on smaller sizes

• Fix "remove" buttons
• New responsive layout using CSS grid
• Fix title ellipsizing

Remaining issues:

• Fix mcatanzaro's/jbrummer's 2 column issue
• Fix layout when removing a grid item
• Test/fix about:web
• Test/fix about:applications (doesn't seem to work in Flatpak)
• Test/fix about:epiphany (doesn't work for me, but apparently didn't change, see screenshots below)
• Test/fix about:memory
• Fix uneven number of items in 2 column mode