Add a copy URL button to popup search and the manager

BookSync 1.3.1
• Warns you to turn off Firefox's own bookmark sync. If Firefox Sync also syncs bookmarks, it fights BookSync: deleted bookmarks come back and others get duplicated. Settings now shows where to switch it off (about:preferences#sync → Bookmarks), and the popup shows a reminder until you choose "Done, it's off".
• History is shown by day. The settings page groups saved versions under their day. With an updated BookSync server, the history keeps the last version of each day for 30 days.
• Desktop Firefox only. Firefox for Android gives extensions no access to bookmarks, so BookSync can't run there. If it is installed there anyway, it now says so and points to the BookSync Android app, instead of showing "Loading…" forever.
• Settings and the popup show an error if they can't start, instead of staying on "Loading…".

Per-account vault limits, and a storage bar in the popup