Show one-line summary of the current work chain task

**Is your feature request related to a problem? Please describe.**

While the tree view is great for inspecting the current progress as well as outputs of the workchain in detail, it is not ideal for trying to follow the overall progression.

**Describe the solution you'd like**

It would be great if we could translate the current work chain status into a _one line_ summary, akin to:

- Relaxing structure...
- Computing k-points...
- Computing band structure...
- Computing Projected Density of States (PDoS)...

This would be a bit similar to the previously removed process progress bar, however, it would be significantly more insightful.

**Describe alternatives you've considered**

One could try to automatically highlight active processes.

**Additional context**

I started working on this in a stale PR a while back (#145), however, it really only introduces the basic infrastructure, no attempt at generating the actual summary report was made yet.