increase localStorage page history variety

we already summarise lead keyword and section totals for the last 100 articles.

this is to add lead author, blog and series, as well as all the display names

The aim is so later we can use the info to show a "Jump-to" bar on the front based on what users like.

/cc @stephanfowler I'd love some feedback since it's your area of expertise =)
I think summary can be a simple object literal rather than a constructor function. In which case this block can just be `if (summary[metaType]) { //do stuff }`