Quick summary text

[kpitten]

For the quick cost summary, let's change the description that currently reads "Quick summary overview shows the total and discounted intervention costs for the upcoming 10 years." to "The quick cost summary shows annual average costs, 10-year total costs, and other summary cost metrics."

Let's also change "Summary of annual average costs" to "Summary cost estimates"

Finally, and I think I may have already mentioned this, but let's drop the "Intervention year" and "Year" headers, as they don't make sense here.
Thanks!