Nice to have: 'grab' cursor when dragging the graph

[hzeller]

What version of pprof are you using?

Github head.

What UI question did you have in mind ?

Not a bug. This is merely UI idea that came to mind playing with the web-UI, specifically the 'graph' view.

When dragging the graph view, the mouse-cursor stays the same as regular pointer.
However, from a user feedback perspective -- seeing that this is holding the graph and moving it around -- it would be neat if the cursor was changing into the 'grab cursor' symbol (the little hand that 'holds on' to the thing being dragged).

I think the CSS cursor property would be cursor: grabbing.

[talohana]

Should be added in #854

[hzeller]

Thank you!