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 =)

the `gu.history` looks like this now - see below for the summary
```
[  
   {  
      "id":"business/2014/nov/06/morrisons-recovery-sales-supermarket",
      "meta":{  
         "sections":[  
            [  
               "business",
               "Business"
            ]
         ],
         "keywords":[  
            [  
               "business/morrisons",
               "Morrisons"
            ]
         ],
         "authors":[  
            [  
               "profile/juliakollewe",
               "Julia Kollewe"
            ]
         ]
      },
      "timestamp":1415810791141,
      "count":1
   },
   {  
      "id":"uk/business",
      "meta":{  
         "keywords":[  
            [  
               "business/business",
               "Economy"
            ]
         ]
      },
      "timestamp":1415810775810,
      "count":1
   },
   {  
      "id":"culture/tvandradioblog/video/2014/nov/12/monty-python-stephen-hawking-brian-cox-eric-idle-video",
      "meta":{  
         "sections":[  
            [  
               "culture",
               "Culture"
            ]
         ],
         "keywords":[  
            [  
               "culture/monty-python",
               "Monty Python"
            ]
         ],
         "blogs":[  
            [  
               "tvandradioblog",
               "TV and radio blog"
            ]
         ]
      },
      "timestamp":1415810726040,
      "count":2
   }
]
```
thje `gu.history.summary` looks like this:
```
{  
   "sections":{  
      "culture":[  
         "Culture",
         1
      ],
      "business":[  
         "Business",
         1
      ]
   },
   "series":{  

   },
   "keywords":{  
      "culture/monty-python":[  
         "Monty Python",
         1
      ],
      "business/business":[  
         "Economy",
         1
      ],
      "business/morrisons":[  
         "Morrisons",
         1
      ]
   },
   "authors":{  
      "profile/juliakollewe":[  
         "Julia Kollewe",
         1
      ]
   },
   "blogs":{  
      "tvandradioblog":[  
         "TV and radio blog",
         1
      ]
   },
   "count":3
}
```