SVG favicons are unsupported (and ignored by the crawler)

[calpaterson]

Description

PIL (pillow) doesn't support SVGs, only raster image formats, and as a result Quarchive doesn't support them either.

Steps to reproduce

1. Bookmark a page with an SVG favicon (eg https://ft.com)
2. Look at your bookmarks

Expected result

Our icon generated from SVG

Actual result

Our icon sometimes slightly blurry, even when there's a vector source

Additional details