Fix Surface task panel shortcut use to use Widget context

The Delete key shortcut of the three different panels in the
Surface Workbench TaskFilling sidebar conflicted between
the panels if multiple were showing. This is resolved by
making the QAction's context the widget, rather than the window.

src/Mod/Surface/Gui/TaskFilling.cpp

@@ -272,6 +272,7 @@ FillingPanel::FillingPanel(ViewProviderFilling* vp, Surface::Filling* obj)
     // Create context menu
     QAction* action = new QAction(tr("Remove"), this);
     action->setShortcut(QString::fromLatin1("Del"));
+    action->setShortcutContext(Qt::WidgetShortcut);
     ui->listBoundary->addAction(action);
     connect(action, SIGNAL(triggered()), this, SLOT(onDeleteEdge()));
     ui->listBoundary->setContextMenuPolicy(Qt::ActionsContextMenu);

src/Mod/Surface/Gui/TaskFillingEdge.cpp

@@ -128,6 +128,7 @@ FillingEdgePanel::FillingEdgePanel(ViewProviderFilling* vp, Surface::Filling* ob
     // Create context menu
     QAction* action = new QAction(tr("Remove"), this);
     action->setShortcut(QString::fromLatin1("Del"));
+    action->setShortcutContext(Qt::WidgetShortcut);
     ui->listUnbound->addAction(action);
     connect(action, SIGNAL(triggered()), this, SLOT(onDeleteUnboundEdge()));
     ui->listUnbound->setContextMenuPolicy(Qt::ActionsContextMenu);

src/Mod/Surface/Gui/TaskFillingVertex.cpp

@@ -127,6 +127,7 @@ FillingVertexPanel::FillingVertexPanel(ViewProviderFilling* vp, Surface::Filling
     // Create context menu
     QAction* action = new QAction(tr("Remove"), this);
     action->setShortcut(QString::fromLatin1("Del"));
+    action->setShortcutContext(Qt::WidgetShortcut);
     ui->listFreeVertex->addAction(action);
     connect(action, SIGNAL(triggered()), this, SLOT(onDeleteVertex()));
     ui->listFreeVertex->setContextMenuPolicy(Qt::ActionsContextMenu);