[EngCom] Public Pull Requests - 2.2-develop

Accepted Public Pull Requests:
 - magento/magento2#13174: Fix: remove TestObserver class (by @Coderimus)
 - magento/magento2#13155: Optimization: module-sales is_null change to strict comparison instead (by @Coderimus)
 - magento/magento2#13171: Optimization: magento/module-catalog is_null change to strict comparison (by @Coderimus)
 - magento/magento2#13170: Optimization: magento/module-tax is_null change to strict comparison (by @Coderimus)
 - magento/magento2#13169: Optimization: magento/module-eav is_null change to strict comparison … (by @Coderimus)
 - magento-engcom/magento2ce#1216: #8453: [GitHub] Price outlining in Invoice PDF (by @serhii-balko)
 - magento/magento2#12990: [2.2.x] Fix undeclared dependency magento/zendframework1 by magento/framework (by @ihor-sviziev)
 - magento/magento2#12998: Make customer name link to customer dashboard (by @srenon)
 - magento/magento2#13086: Add failsafe to items.phtml (by @samgranger)
 - magento/magento2#13066: Fix for #12877 as per @azeemism (by @jagritijoshi)
 - magento/magento2#13033: Newsletter\Model\Subscriber::loadByEmail() does not use MySQL index (by @devamitbera)
 - magento-engcom/magento2ce#1032: magento/magento2#8114: "Save Block"-button on Add New Block silently ignores clicks if the content is empty. (by @RomaKis)


Fixed GitHub Issues:
 - magento/magento2#8453: Price outlining in Invoice PDF (reported by @joost-florijn-kega) has been fixed in magento-engcom/magento2ce#1216 by @serhii-balko in 2.2-develop branch
   Related commits:
     1. 21566e89

 - magento/magento2#12967: Undeclared dependency magento/zendframework1 by magento/framework (reported by @linden2015) has been fixed in magento/magento2#12990 by @ihor-sviziev in 2.2-develop branch
   Related commits:
     1. df2c8fda

 - magento/magento2#12877: [2.2.1] Magento Database Backup Command Fails (Fix included) (reported by @azeemism) has been fixed in magento/magento2#13066 by @jagritijoshi in 2.2-develop branch
   Related commits:
     1. bc434c1b

 - magento/magento2#12787: Newsletter\Model\Subscriber::loadByEmail() does not use MySQL index (reported by @schmengler) has been fixed in magento/magento2#13033 by @devamitbera in 2.2-develop branch
   Related commits:
     1. 75597839
     2. b8534974
     3. be8b258b

 - magento/magento2#8114: "Save Block"-button on Add New Block silently ignores clicks if the content is empty. (reported by @geon) has been fixed in magento-engcom/magento2ce#1032 by @RomaKis in 2.2-develop branch
   Related commits:
     1. 5bac54fc
     2. 4456872b
     3. 42ee7cc8