Add config to specify a default dashboard layout

Signed-off-by: Julius Härtl <jus@bitgrid.net>

apps/dashboard/lib/Controller/DashboardController.php

@@ -99,7 +99,8 @@ class DashboardController extends Controller {
 
 		$this->eventDispatcher->dispatchTyped(new RegisterWidgetEvent($this->dashboardManager));
 
-		$userLayout = explode(',', $this->config->getUserValue($this->userId, 'dashboard', 'layout', 'recommendations,spreed,mail,calendar'));
+		$systemDefault = $this->config->getAppValue('dashboard', 'layout', 'recommendations,spreed,mail,calendar');
+		$userLayout = explode(',', $this->config->getUserValue($this->userId, 'dashboard', 'layout', $systemDefault));
 		$widgets = array_map(function (IWidget $widget) {
 			return [
 				'id' => $widget->getId(),