renderer: keep frames in vram while paused

Saves some GPU cycles when adjusting parameters.

app/project/item/footage/imagestream.cpp

@@ -120,6 +120,12 @@ void ImageStream::set_colorspace(const QString &color)
   emit ParametersChanged();
 }
 
+QString ImageStream::get_colorspace_match_string() const
+{
+  return QStringLiteral("%1:%2").arg(footage()->project()->color_manager()->GetConfigFilename(),
+                                     colorspace());
+}
+
 void ImageStream::ColorConfigChanged()
 {
   ColorManager* color_manager = footage()->project()->color_manager();

app/project/item/footage/imagestream.h

@@ -48,6 +48,8 @@ public:
   const QString& colorspace(bool default_if_empty = true) const;
   void set_colorspace(const QString& color);
 
+  QString get_colorspace_match_string() const;
+
 protected:
   virtual void FootageSetEvent(Footage*) override;