feat(19.6.1-01): Administrators screen and cross-controller record actions

- pact.HasAdminActionExtensions / AdminActionExtension: plugins add record
  actions to any admin controller by ID, merged at boot before permission
  validation (unknown target, no preview, duplicate name stop the boot)
- internal summercms.cabana pseudo-plugin, appended only when some plugin
  registers admin controllers: Administrators list and preview, settings
  link under System, backend.manage_users and backend.manage_roles with no
  role grants
- backend::lang user, user.role and permissions copy (en, pl)
- smoke tests: compile-time seam and settings, Postgres list/preview/action

modules/cabana/backendscreens/controllers/users/config_form.yaml

@@ -0,0 +1,16 @@
+name: backend::lang.user.name
+form: ~/plugins/summercms/cabana/models/user/fields.yaml
+modelClass: Backend\Models\User
+defaultRedirect: summercms/cabana/users
+
+update:
+    redirect: summercms/cabana/users/update/:id
+    redirectClose: summercms/cabana/users/preview/:id
+
+preview: {}
+
+messages:
+    update: backend::lang.messages.form.update
+    saved: backend::lang.messages.form.saved
+    edit: backend::lang.user.edit
+    preview: backend::lang.user.preview

modules/cabana/backendscreens/controllers/users/config_list.yaml

@@ -0,0 +1,11 @@
+list: ~/plugins/summercms/cabana/models/user/columns.yaml
+modelClass: Backend\Models\User
+title: backend::lang.user.list_title
+recordUrl: summercms/cabana/users/preview/:id
+noRecordsMessage: backend::lang.user.list_empty
+recordsPerPage: 20
+showSetup: true
+
+toolbar:
+    search:
+        prompt: backend::lang.list.search_prompt