Translation Manager: coverage report, backoffice settings, UI tidy

Released 17.11.1
New Translation Coverage tab for sets, including Library element sets
Core settings are saved in the database and edited in the backoffice
Quick translate is on in the starter set
UI tidied across the dashboard, jobs, items, sets, glossary/memory, connectors, dialogs and settings, with consistent wording, empty states and paging
The item view shows block values as blocks
Umbraco.AI sites are pointed at the Umbraco.AI connector, with a banner on the Connectors page
Fixes: sites upgraded from v17 can run the v18 migration plan; culture version lookups filtered by culture