Status bar: load actual total rows in background while approximate total is shown

[dismantl]

Right now, because it can take a while to count the actual number of rows in a large table, at first it shows the "approximate total rows" in the status bar until you filter a column or load additional rows in which case it will load the actual total. The approximation queries the Postgres pg_class table because it returns super quickly: SELECT reltuples FROM pg_class WHERE oid = '{table_name}'::regclass.

It would be ideal to load the actual total in the background after the approximate total is shown, and replace it once the query returns. Also for tables with very few rows, the approximate total will return zero, in which case the approximate total should be skipped and only the actual total should be shown.