Issue #2058321 by tim.plunkett, pameeela: Move the 'place block' UI into the block listing.

core/modules/block/block.admin.inc

core/modules/block/block.module

core/modules/block/block.routing.yml

core/modules/block/css/block.admin.css

...modules/block/custom_block/custom_block.local_actions.yml

core/modules/block/custom_block/custom_block.module

core/modules/block/lib/Drupal/block/BlockListController.php

...b/Drupal/block/Controller/BlockAutocompleteController.php

core/modules/block/lib/Drupal/block/Form/PlaceBlocksForm.php

...odules/block/lib/Drupal/block/Routing/RouteSubscriber.php

...s/block/lib/Drupal/block/Tests/BlockLanguageCacheTest.php

...s/block/lib/Drupal/block/Tests/BlockLibrarySearchTest.php

core/modules/block/lib/Drupal/block/Tests/BlockTest.php

...odules/block/lib/Drupal/block/Tests/BlockTitleXSSTest.php

core/modules/block/lib/Drupal/block/Tests/BlockUiTest.php

.../modules/block/tests/modules/block_test/block_test.module

core/modules/menu/lib/Drupal/menu/Tests/MenuTest.php

core/modules/system/css/system.plugin.ui.css

...system/lib/Drupal/system/Plugin/Block/SystemMenuBlock.php

core/modules/system/system.module