Live blogs: Hide contributor image if multiple. Restore comment icon in header

Before:
![screen shot 2014-10-23 at 12 22 58](https://cloud.githubusercontent.com/assets/813383/4752132/8ff82f24-5aa7-11e4-8723-23d9ea00b05e.png)

![screen shot 2014-10-23 at 12 25 12](https://cloud.githubusercontent.com/assets/813383/4752138/a5285a0e-5aa7-11e4-8a1a-8faeec84cb32.png)

After:

![screen shot 2014-10-23 at 12 24 51](https://cloud.githubusercontent.com/assets/813383/4752133/947a5cfc-5aa7-11e4-970a-c146ae524fa5.png)

![screen shot 2014-10-23 at 12 25 03](https://cloud.githubusercontent.com/assets/813383/4752137/9e5ac504-5aa7-11e4-951e-eb2fd0423f65.png)

/cc @mattosborn @cantlin 
I think we can use `contributors.length == 1` here as showBylinePic will return false when there is a single contributor but the byline doesn't match their name exactly (e.g. "John Smith in London" would return false when really we want to show the byline pic)