Fix subtitles for CDS story

What does this PR do?

Adds periods to subtitles that did not have it and added a subtitle to the last chart.

"The makeup of the undergraduate student population had not significantly changed in the last three years."

All steps should be completed in the order presented, and you should not move on to the next step until the previous is completed.

[x] The title of the html page is the same as the chart.
[x] The meta_data.json file is filled in correctly (the description is a complete sentence, the title is the same as the visual).
[x] The chart and its associated pages have been minified using the npm run process-visual command.
[x] The visual is styled similar to other charts (centered title/subtitle, no legends unless absolutely necessary, etc.)
[ ] This visual was approved by the lead developer.
[x] The visual was approved by the story's stakeholders.