Expandable summary

- [new] Summaries are expandable
- [new] Sharing buttons are below the summary in the right column, with a title to separate the two: "Share this live blog"
- [removed] toggle (show/hide) summary on mobile: the logic in the CSS was becoming too complicated. We can put it back later with some more JS instead of relying exclusively on CSS classes if necessary.


![summary-mobile-expandable](https://f.cloud.github.com/assets/85783/1131320/74bccbfe-1bb8-11e3-9468-9cca938f294f.gif)

![summary-ipad-expandable](https://f.cloud.github.com/assets/85783/1131323/78091204-1bb8-11e3-9a5c-4fbb5bae97d2.gif)

![ ](http://s2.developerslife.ru/public/images/gifs/56f117c4-d57e-404c-b5d9-ff61db1b9150.gif)