Post detail toolbar improvements

This is a small PR that updates a few things in the post detail view toolbar:

 * Changed the touch targets to be 48x48dp.
 * Fixed ugly orange background color when a toolbar button was tapped.
 * Fixed tint of comment button.

Before:
![cool](https://f.cloud.github.com/assets/789137/2465235/3064ee9c-afa0-11e3-833a-5dfe33b1be9d.jpg)
After:
![cool2](https://f.cloud.github.com/assets/789137/2465237/357e23ee-afa0-11e3-9eca-f1f20bf43941.jpg)