Added dashboard tab selecting to pageview analytics.

This will track tab changes as new pageviews. One issue is that the tabs are currently named e.g. "#tab2", "#tab3", etc., so in the pageview analytics, these pageviews will show up as "/dashboard#tab2", etc., which might not mean anything to the staff looking at the analytics.

Do you want me to go ahead and rename the tabs to something more meaningful along with this too?