Event Time and Last Event display without values in List view

[labuchholz]

Describe the bug
Event Time and Last Event display blank in List view, even when there's values in "Last Action" and "What" in single submission View.

(I'm assuming 'Last Event' in List = "What" in single submission view, and Event Time in List = Last Action in single submission view.)

To Reproduce
Steps to reproduce the behavior:

1. Go to 'admin/list'
2. Click on 'Customize columns'
3. Add Event Time and Last Event to Displayed Columns, save
4. See blanks in List

Expected behavior
The Event Time column in List view should display the date/time of the last event, same as in single submission view. The Last Event column in List view should display the same values as appears under “What” in single submission view.

If I'm misinterpreting the purpose of these columns, then the request changes to: In List view, the ability to display and sort the values found in "Last Action" and "What" in single submission view.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
We're self hosted, version 4.2.4

Since we can’t trigger any notifications without a status change, this means that we don’t see comments added to a submission--the student has to contact us via other means. So we want to be able to quickly scan the values in Last Action and Last Event to check if someone has written a message. See feature request: #1926