Adjust "Top Pages" in right hand column toggle

[tdlowden]

When someone clicks on 7 days or 30 Days, the reports switch from being page-based (in the Now chart) to domain-based. Unfortunately, the language at the top of the chart that says Top Pages is currently static, no matter which chart a user is viewing. We need to alter the Top Pages heading on the chart to change to Top Sites or Top Domains when a user clicks 7 Days or 30 Days.

[lauraGgit]

Probably can't add a test to this unless we also build out headless browser testing, which would be ideal, but a big lift in addition to the unit tests I added in #531