optimizations - improved prefetch strategy

[gibkigonzo]

Related Issues

related #4030 - it's not closing this issue

Short Description and Why It's Useful

• add v-lazy for ProductImage => faster onload, we don't need to wait for all images
• move common libraries from app.js to vendor.js - faster we get app.js, then faster app will be loaded. vendor.js has now same weight as app.js. When app.js will be lighter then vendor.js, then we can split vendor.
• remove product carousel chunk - we use it only on product page so this script can be in vsf-product chunk.
• move loading google fonts to head

Screenshots of Visual Changes before/after (if There Are Any)

Tested on /women/women-20
Before:

After:

Which Environment This Relates To

Check your case. In case of any doubts please read about Release Cycle

• Test version (https://test.storefrontcloud.io) - this is a new feature or improvement for Vue Storefront. I've created branch from develop branch and want to merge it back to develop
• RC version (https://next.storefrontcloud.io) - this is a stabilisation fix for Release Candidate of Vue Storefront. I've created branch from release branch and want to merge it back to release
• Stable version (https://demo.storefrontcloud.io) - this is an important fix for current stable version. I've created branch from hotfix or master branch and want to merge it back to hotfix

Upgrade Notes and Changelog

• No upgrade steps required (100% backward compatibility and no breaking changes)
• I've updated the Upgrade notes and Changelog on how to port existing Vue Storefront sites with this new feature

IMPORTANT NOTICE - Remember to update CHANGELOG.md with description of your change

Contribution and Currently Important Rules Acceptance

• I read and followed contribution rules