fix/v2 migration

[iansinnott]

Update how the v1 -> v2 migration works. It now runs through the main browser tab, asking the user to perform the migration.

This also cleans up some things like the storage and notification permissions, which are not needed.

• do not require notification permissions
• fix bug where query would not reset in URL if empty
• WIP cleanup flawed migration logic
• add separate backend adapter for ease of testing
• better testability
• WIP bump version and incrementally import from vlcn
• further error handling for failed fetches
• remove unused hook
• add a modal for migrations
• update when the migration modal shows
• no more dumping and loading data dir
• add a timeout before checking migration status
• hide migration modal after migration