Information panel for current state of the notebooks

[pankgeorg]

We can inform the user about information that is interesting like

About the system

• % available CPU, memory
• Whether Pluto is to blame for high %CPU/MEM (or there is high system load)
• Extra system info

About Pluto

• How many cells are still running
• How much time is the current cell executing for
• expected (?) time to end of time

This may be too busy/flashy if it shows up too fast, so we probaly want to debounce it for a few seconds.