Improve the visualizations of differences

[tfiedor]

Based on the feedback from the Lunch And Learn, we should extend our showdiff with the following:

• [x] Scale the rectangles based wrt biggest profile
• [x] #242
• [ ] Add collapsing section with basic metrics (top metrics, number of functions, number of levels, maximal traces, number of unique traces, etc.)
• [x] Add exit code to the display
• [x] Add ? to tooltips, so it is clear there is something helpful
• [x] Add synchronized progress in flamegraphs (however, is this even possible???)