Implement Alt Click to default on sliders

The following sliders now have Alt Click functionality:
 - Nodes (What it's initialy set too or 0 if not)
 - Export Dialog Dimensions~ (Defaults to Sequence width/height)
 - Export Compression Settings~
    - Advanced (0)
 - Speed/Duration
    - Speed (100%)
    - Duration (clip length)
 - Stream Properties Image sequence
    - Start Index (1)
    - End Index (sequence length)

Sliders with no default value set ignore an Alt
Click.

Added SliderBase::SetDefaultValue() which sets the
default value of a slider.

Added ValueReset() to SliderBase signals which is
called if a slider is Alt Clicked on. Only updates
if default_value_ is not Null.

app/widget/nodeparamview/nodeparamviewwidgetbridge.cpp

@@ -66,6 +66,7 @@ const QList<QWidget *> &NodeParamViewWidgetBridge::widgets() const
 
 void NodeParamViewWidgetBridge::CreateWidgets()
 {
+
   if (input_->IsArray()) {
 
     NodeParamViewArrayWidget* w = new NodeParamViewArrayWidget(static_cast<NodeInputArray*>(input_));
@@ -91,6 +92,11 @@ void NodeParamViewWidgetBridge::CreateWidgets()
     case NodeParam::kInt:
     {
       IntegerSlider* slider = new IntegerSlider();
+      if (!input_->get_standard_value().isNull()) {
+        slider->SetDefaultValue(input_->get_standard_value());
+      } else {
+        slider->SetDefaultValue(0);
+      }
       widgets_.append(slider);
       connect(slider, &IntegerSlider::ValueChanged, this, &NodeParamViewWidgetBridge::WidgetCallback);
       break;
@@ -363,6 +369,11 @@ void NodeParamViewWidgetBridge::CreateSliders(int count)
 {
   for (int i=0;i<count;i++) {
     FloatSlider* fs = new FloatSlider();
+    if (!input_->get_standard_value().isNull()) {
+      fs->SetDefaultValue(input_->get_split_standard_value().at(i));
+    } else {
+      fs->SetDefaultValue(0.0f);
+    }
     widgets_.append(fs);
     connect(fs, &FloatSlider::ValueChanged, this, &NodeParamViewWidgetBridge::WidgetCallback);
   }