config_readonly 8.x-1.0-beta3

Changes since 8.x-1.0-beta2:

• #2826274 by scott_euser, Manuel Garcia, bircher, douggreen, GaëlG: Config whitelist to allow "some" configuration to be edited while lock is active
• #2734591 by charginghawk, pwolanin: Document how to enable config changes or toggle read-only via drush or cli
• #2734591 by pwolanin: Document how to enable config changes or toggle read-only via drush or cli
• Revert "Issue #2734591 by pwolanin: Document how to enable config changes or toggle read-only via drush or cli"
• #2734591 by pwolanin: Document how to enable config changes or toggle read-only via drush or cli
• #2851929 by gambry: fix for ReadOnlyConfigTest fails when using core 8.3.x or 8.4.x branches
• Small doxygen cleanup of \Exception class name
• #2792837 by reekris: Add permissions admin form to config readonly check
• #2794413 by GaëlG, scott_euser: prevent search form from being locked to work around a core bug