[assist] Show database comment as tooltip in editors

Using the query editors for Hive and Impala in Hue I notice that the tooltip for tables in the list of tables to the left shows the table name itself. I think it would be more beneficial if this tooltip showed the comment attached to the table (if present). Similarly when hovering a database in the same list it could show the comment attached to the database (if present). Currently there is no tooltip at all for databases.