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 =)
Agree this is a rather weird pattern. You could include lodash `omit` and do this:
```
preparePage: function (page) {
    return {
        id: '/' + page.pageId,
        meta: omit({
            section: [page.section, page.sectionName],
            series: [page.seriesId, page.series],
            leadKeyword: [getHead(page.keywordIds), getHead(page.keywords)],
            leadAuthor: [getHead(page.authorIds), getHead(page.author)],
            leadBlog: [getHead(page.blogIds), getHead(page.blogs)]
        }, function(pair) {
            return !pair[0] || !pair[1];
        })
    };
}
```
Declare the `getHead` utility outside of the function that uses it - as a normal js practice. Also `preparePage` is a utility that shouldn't be included in this module's returned obj. (Once you've brought that stuff in from common.js as per Patricks comment.)