fix is.nan bug in Debugging sub-tab
redesign Details tab calls
new details=TRUE, details.on.tab.sel=TRUE
trigger updates to Details intelligently (avoid unnecessary calls)
allow to update Details only when selecting the tab
Full data frame details are computed only once
request confirmation when loading big data frame (>500,000 cells)
input boxes: red-ish background when no completion available
similar to Geany
rm commented out Structure tab: not for upcoming release
speed-up: catch if row_filter outputs all FALSE or empty selection