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 am setting things on `this`... I got this snippet from stack overflow somewhere as a way to optionally set a load of properties on a new object.
http://stackoverflow.com/questions/18019854/conditionally-set-a-json-object-property
In JS it seems to be common to have a function that you use the new keyword with, that will make a new object.  This is just an inline equivalent.  However it clearly is weird and confusing to JS programmers, so tomorrow we can rewrite it if you can spare some time? =)