File: Provide percent missing values in Info box

[stuart-cls]

Hi,

The Data Table widget provides a nice overview of the dataset in the "Info" box, specifically including the percent missing values. It would be nice if the File widget "Info" box did the same to help diagnosing problematic datasets.

Thanks!

Orange version

3.14.0

Expected behavior

File "Info" box provides the same text as Data Table "Info" box.

Actual behavior

File "Info" has less info.

Steps to reproduce the behavior

Additional info (worksheets, data, screenshots, ...)

[rokgomiscek]

Closed via #3305