Improve progress bar

[mstykow]

Is your feature request related to a problem? Please describe.
The progress bar has a few areas that could be improved:

• the rightmost color in the stacked bar looks like empty space rather than a color
• hovering over the progress bar, there is no indication as to which color belongs to which statement/count and some colors are not represented at all (the signals progress bar contains four colors but only three statements)
• hovering over the progress bar, there is no message what will happen when I click on the progress bar

Describe the solution you'd like
I see two options:

1. Replace the entire bar by a proper library to render a stacked bar chart. The one I like most is this one: https://nivo.rocks/bar/ Notice how this bar chart has nice (customizable) tooltips when you hover over a part of the stacked bar chart. This means we could offer different kinds of click actions depending on which part of the bar is clicked, in addition to having just a better display.
2. Sticking with the current progress bar design, we could exchange just the current tooltip for a MUI Popover which contains information similar to how the tooltip of option 1. looks like, i.e., a colored box followed by a title and a count. The popover would allow us to render custom content and not just text, unlike the current tooltip.