began UI for keyframing

Largely extending the existing NodeParamView with functionality from the
previous release.

app/widget/nodeparamview/nodeparamviewundo.cpp

@@ -0,0 +1,19 @@
+#include "nodeparamviewundo.h"
+
+NodeParamSetKeyframing::NodeParamSetKeyframing(NodeInput *input, bool setting, QUndoCommand *parent) :
+  QUndoCommand(parent),
+  input_(input),
+  setting_(setting)
+{
+  Q_ASSERT(setting != input_->is_keyframing());
+}
+
+void NodeParamSetKeyframing::redo()
+{
+  input_->set_is_keyframing(setting_);
+}
+
+void NodeParamSetKeyframing::undo()
+{
+  input_->set_is_keyframing(!setting_);
+}