Link default content styles through RL

This patch adds a simple & somewhat hacky link to the standard content styles
in the head of our HTML. This lets us check the rendering of Parsoid content
visually, and identify issues in the Parsoid-specific styling.

Bug: 51245
Change-Id: I19afe270188be8299784d18ff2b6f7f027e7ea9d
Merge "Link default content styles through RL"