fully implemented setting keyframes and standard values in the NodeParamView

Widget now supports creating keyframe and standard values, supports dragging
from sliders (not creating an undo command for each drag), and everything is
undoable.

app/node/input.h

@@ -179,6 +179,11 @@ signals:
   void KeyframeRemoved(NodeKeyframePtr key);
 
 private:
+  /**
+   * @brief Returns whether a data type can be interpolated or not
+   */
+  static bool type_can_be_interpolated(DataType type);
+
   /**
    * @brief We use Qt signals/slots for keyframe communication but store them as shared ptrs. This function converts
    * a raw ptr to a list index