Catch exceptions from the http client.
Fix type hint, and thus crawling for favicons.
Allow passing in a bookmark creation date when creating a bookmark.
First stab at importing bookmarks.

Adds an importer for the JSON format used by Firefox/Mozilla. Creates tags
for each parent folder in the bookmark hierarchy exported by Firefox. The
crawl task seems to take *forever* though - might need to turn this off for
imports? Thought this shouldn't run until after the request is complete?