Fix Printing Styles

Changed media=screen to media=all in stylesheet links for Invoice and
Dispatch Note template files so that styles are maintained when printing
from a browser.
changed all occurrences of insert to add
https://github.com/opencart/opencart/issues/2290
Merge pull request #2288 from uksitebuilder/Fix-Invoice-and-Shipping-Note-Print-Styles

Fix Printing Styles