#381 Improve use of Status Line

[Ronald]

The status line in the bottom is currently, to the most part, unused space (it mainly display the window size).

I could see two ways to make it useful:

- Provide an interface so that 3rd party applications can display/control part of the status lines (similar to add-ons in web browsers); for example, such an add-on could continuously display the time of the day in the status line.

- Provide an tool (executable program) with which a user can display an arbitrary text in the status line. Such a tool could be used from (say) a long-running Windows batch file to display the progress of the batch execution.