Fix missing image in Scenario Viewer detailed instructions

[dflynn-volpe]

In detailed instructions popup for the Scenario Viewers, need to make sure the following .png image exists in the img directory.

       <p>The levels are displayed in scenario bar charts, one for each category, as shown in the following illustration.</p>
       <img src="img/verpat-barchartscen.png" width="95%">

Issue raised by @mrspeel

[jrawbits]

We need to revisit the popup instructions comprehensively for the "next generation" (3.0) viewer. I'd like to rotate them out of the HTML file into other assets (e.g. by adding Javascript to populate the modal popup div's in the HTML from a file - need to explore what's possible there, since loading files inside javascript is strongly discouraged). None of that probably needs to be "dynamic". I'd just like a better place to edit the individual pop-ups that is not the main HTML file.