implemented value node

Also implements changes necessary to support an input data type
that changes. Much of that foundation was built in
`nodearchchanges`, but hadn't been finalized. This commit
finalizes and provides a reference implementation/test with the
"Value" node.

Fixes #1443

app/node/factory.cpp

@@ -46,6 +46,7 @@
 #include "project/folder/folder.h"
 #include "project/footage/footage.h"
 #include "project/sequence/sequence.h"
+#include "node/input/value/valuenode.h"
 
 namespace olive {
 QList<Node*> NodeFactory::library_;
@@ -234,6 +235,8 @@ Node *NodeFactory::CreateFromFactoryIndex(const NodeFactory::InternalID &id)
     return new Folder();
   case kProjectSequence:
     return new Sequence();
+  case kValueNode:
+    return new ValueNode();
 
   case kInternalNodeCount:
     break;