Add header bar first link left padding

The first link in the top bar is nudged right against the border of my monitor. On my laptop, it appears cut off a little (the plastic border overlaps the LCD). It also just looks better.

Before:
![reddit before](https://cloud.githubusercontent.com/assets/4472083/3126338/faafb7be-e79e-11e3-9090-5fed8164973b.png)
After:
![reddit after](https://cloud.githubusercontent.com/assets/4472083/3126341/ff5f922a-e79e-11e3-9caa-e533fabf29a3.png)

I added a `padding-left` of 4px. I used the `first-child` pseudo-element selector to ensure future proofing (any link there will also have that padding).