Consider adding image preview support to places

[mhammond]

Bug 1742558 added image preview support to desktop places. We might end up needing something similar for our tabs work, so should see if we can get inspiration from that bug. Of note:

• This is a different problem from syncing favicons - the preview url isn't synced.
• desktop already has "page thumbnails" support which is the basis for this, so there might not be much to steal other than the sql schema (and it's not even clear the schema changes?)

┆Issue is synchronized with this Jira Task