Use Alchemy::Current if supported

Since Alchemy 7.1 `Alchemy::Language.current` is deprecated.
We should use `Alchemy::Current` if present in the Alchemy version.

app/controllers/alchemy/json_api/admin/pages_controller.rb

@@ -17,7 +17,11 @@ def caching_options
         end
 
         def set_current_preview
-          Alchemy::Page.current_preview = @page
+          if Alchemy.const_defined?(:Current)
+            Alchemy::Current.preview_page = @page
+          else
+            Alchemy::Page.current_preview = @page
+          end
         end
 
         def last_modified_for(page)

app/controllers/alchemy/json_api/pages_controller.rb

@@ -120,9 +120,17 @@ def api_page(page)
       def base_page_scope
         # cancancan is not able to merge our complex AR scopes for logged in users
         if can?(:edit_content, ::Alchemy::Page)
-          Alchemy::Language.current.pages.joins(page_version_type)
+          current_language.pages.joins(page_version_type)
         else
-          Alchemy::Language.current.pages.published.joins(page_version_type)
+          current_language.pages.published.joins(page_version_type)
+        end
+      end
+
+      def current_language
+        if Alchemy.const_defined?(:Current)
+          Alchemy::Current.language
+        else
+          Alchemy::Language.current
         end
       end
 

spec/controllers/alchemy/json_api/admin/pages_controller_spec.rb

@@ -17,7 +17,7 @@
 
     it "stores page as preview" do
       get :show, params: { path: page.urlname }
-      expect(Alchemy::Page.current_preview).to eq(page.id)
+      expect(Alchemy::Current.preview_page).to eq(page)
     end
   end
 end