Aggregation for graphs in collapsed processes

[stdedos]

Even though System is at almost 80%, it's corresponding graph is empty:

I understand that there could be a lot of complexity into it to fix it properly (that you may not want to go), and if so: can you at least make the graph an "indicator" of the current collapsed node's sum?

Even though I have (a lot) of columns, it is usually easier to visually identify the curlprit who is eating the resources.

Related issues: #99 #192