Update product.tpl

Added check for guest reviews.  Display login prompt if guest review is disabled.
Update changelog.md
Update common.js

Removed the clear fix in grid script and added after the ready function
Opencart 2.0 paypal_order field date_modified error #2036
Merge pull request #2040 from gortsilas/patch-1

Opencart 2.0 paypal_order field date_modified issue #2036
Merge pull request #2039 from latestthemes/master

Update common.js
Merge pull request #2026 from OpenCartAddons/master

Update product.tpl
Merged master fixed conflict.