Add print plugin, use npm package via yarn

[thet]

• Add the print plugin per default, so that images are loaded before the page is going to be printed.
• Use the npm package and yarn to install lazysizes for a defined way to update / add resources. Via .yarnrc a custom location instead node_modules is defined.

Fixes https://github.com/collective/collective.lazysizes/issues/50

[thet]

travis tests are failing in the moment because of the Plone 4.3 integration.

I don't like having the jsregistry.xml GS profile file around for Plone 5.x - this is registering the resources into the plone-legacy bundle - along with the registration of the lazysizes bundle. That way we end up with a double reigstration of these resources. I'd actually vote to remove the Plone 4.3 support. Or doing the registration with separate 4.3 and 5.x profiles, as I did for my initial Plone 5.x support PR.

Any comments?

[rodfersou]

please, use sc.recipe.staticresources https://github.com/simplesconsultoria/sc.recipe.staticresources and webpack for this (we are migrating all of our addons to use it)

[hvelarde]

superseded by #59