Merging print.css into frontend.css

[dparker1005]

All Submissions:

• Have you followed the Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Consolidating print.css into frontend.css.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you successfully run tests with your changes locally?

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

[kimcoleman]

I feel that there is very little concern someone made a local print.css file - but since it is "possible" we have backwards incompatible changes, would this force this to be 3.1? I'm good with either case. I have very little confidence anyone has a custom location print.css since it was just one line.