panels: implement a small margin on all panels to ensure the focus border is always visible

app/panel/node/node.cpp

@@ -32,7 +32,7 @@ NodePanel::NodePanel(QWidget *parent) :
   connect(node_view_, SIGNAL(SelectionChanged(QList<Node*>)), this, SIGNAL(SelectionChanged(QList<Node*>)));
 
   // Set it as the main widget of this panel
-  setWidget(node_view_);
+  SetWidgetWithPadding(node_view_);
 
   // Set strings
   Retranslate();

app/panel/pixelsampler/pixelsamplerpanel.cpp

@@ -26,7 +26,7 @@ PixelSamplerPanel::PixelSamplerPanel(QWidget *parent) :
   PanelWidget(QStringLiteral("ProjectPanel"), parent)
 {
   sampler_widget_ = new ManagedPixelSamplerWidget();
-  setWidget(sampler_widget_);
+  SetWidgetWithPadding(sampler_widget_);
 
   Retranslate();
 }

app/panel/project/project.cpp

@@ -40,8 +40,6 @@ ProjectPanel::ProjectPanel(QWidget *parent) :
   // Create main widget and its layout
   QWidget* central_widget = new QWidget(this);
   QVBoxLayout* layout = new QVBoxLayout(central_widget);
-  layout->setMargin(0);
-  //layout->setSpacing(0);
   setWidget(central_widget);
 
   // Set up project toolbar

app/panel/timebased/timebased.cpp

@@ -153,7 +153,7 @@ void TimeBasedPanel::SetTimeBasedWidget(TimeBasedWidget *widget)
     connect(widget_, &TimeBasedWidget::TimebaseChanged, this, &TimeBasedPanel::TimebaseChanged);
   }
 
-  setWidget(widget_);
+  SetWidgetWithPadding(widget_);
 }
 
 void TimeBasedPanel::Retranslate()

app/panel/tool/tool.cpp

@@ -33,7 +33,7 @@ ToolPanel::ToolPanel(QWidget *parent) :
   t->SetTool(Core::instance()->tool());
   t->SetSnapping(Core::instance()->snapping());
 
-  setWidget(t);
+  SetWidgetWithPadding(t);
 
   connect(t, &Toolbar::ToolChanged, Core::instance(), &Core::SetTool);
   connect(Core::instance(), &Core::ToolChanged, t, &Toolbar::SetTool);