Add print media rules

[phaux]

This makes a page using paper-header-panel + paper-drawer-panel printable. Without these rules it prints only the first page.

Related: https://github.com/PolymerElements/paper-header-panel/pull/91

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[phaux]

I signed it

[googlebot]

CLAs look good, thanks!

[blasten]

minor comment, otherwise LGTM

[phaux]

Done