refactor: put resource downloading classes in common namespace

Puts them all inside the 'ResourceDownload' namespace, so that it's a
bit clearer from the outside that those belong to the same 'module'.

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/ui/dialogs/ResourceDownloadDialog.h

@@ -7,12 +7,15 @@
 #include "ui/pages/BasePageProvider.h"
 
 class ResourceDownloadTask;
-class ResourcePage;
 class ResourceFolderModel;
 class PageContainer;
 class QVBoxLayout;
 class QDialogButtonBox;
 
+namespace ResourceDownload {
+
+class ResourcePage;
+
 class ResourceDownloadDialog : public QDialog, public BasePageProvider {
     Q_OBJECT
 
@@ -53,3 +56,5 @@ class ResourceDownloadDialog : public QDialog, public BasePageProvider {
 
     QHash<QString, ResourceDownloadTask*> m_selected;
 };
+
+}  // namespace ResourceDownload