address 8.x-1.0-beta3

Changes since 8.x-1.0-beta2:

• #2662540 by yanniboi, bojanz: Rewrite CountryConstraintValidatorTest
• #2525762 by dbolinovski, slasher13, rocketeerbkw: Create a Plain formatter
• #2586275 by subhojit777: Disallow creating a zone with a zone_member_zone that references the parent zone
• #2664932 by webflo: Optimize composer package definition with project namespaces
• #2587013 by vasike, bojanz: Create a zone member test
• #2699975 by martin107: csslint One minor nudge
• #2687481 by gokulnk: Add a link to the settings page
• #2735977: Rewrite the README, update Composer requirements
• #2692187 by webflo: Add translation context to string from LabelHelper
• #2686529 by rakesh.gectcr: @file is not required for classes, interfaces and traits
• #2619940 by bojanz, ChristianAdamski: Add a country filter
• #2633912 by bojanz, GoZ: Default country widget summary
• #2626746 by Xano: Expose the zone plugin type
• #2633972 by czigor: Required addressfield has a '- Select -' option
• #2638184 by Xano: Missing check for commerceguys/zone
• Add missing variable hints to make PhpStorm happy.
• #2639072 by heykarthikwithu: Remove depreciated methods and unused imports in code base
• Fix wrong FieldConfigInterface var definition
• #2610974 by czigor: Replace the injected entity manager with the entity type manager
• #2621266 by visabhishek: Spelling mistakes