revert changes of add panel button to require save permission

This resolves an issue where the add panel button was shown on the default home dashboard

public/app/features/dashboard/dashnav/dashnav.html

@@ -17,7 +17,7 @@
 	<div class="navbar__spacer"></div>
 
 	<div class="navbar-buttons navbar-buttons--actions">
-		<button class="btn navbar-button navbar-button--add-panel" ng-show="::ctrl.dashboard.meta.canEdit" bs-tooltip="'Add panel'" data-placement="bottom" ng-click="ctrl.addPanel()">
+		<button class="btn navbar-button navbar-button--add-panel" ng-show="::ctrl.dashboard.meta.canSave" bs-tooltip="'Add panel'" data-placement="bottom" ng-click="ctrl.addPanel()">
 			<i class="gicon gicon-add-panel"></i>
 		</button>