fileserver: browse template SVG icons and UI tweaks (#5812)

* fileserver browse.html UI tweaks: folder-symlink icon, search

fileserver browse.html UI tweaks: folder-symlink icon, search

- ui - add folder-symlink SVG icon
- search: use `<input type="search">` instead of `text`
- fix npe with `sizebar.style.width` = null in grid mode

* tabify whitespace

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

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Co-authored-by: Francis Lavoie <lavofr@gmail.com>