Add jump comments link

Add comment counts to live-blog key events panel
![comment-count](https://cloud.githubusercontent.com/assets/986155/4408978/dd7674ac-44d8-11e4-9918-0c1129a10dd9.png)

@ironsidevsquincy the `tone-global` mixin generates the icon css: https://github.com/guardian/frontend/blob/57bd30ce548ad4932ab99483b8edc39a0ffd9e16/common/app/assets/stylesheets/theme/_tones.scss#L40