nodeview: implemented copying/pasting nodes

Re-uses XML-based project saving/loading functions to store nodes, their
parameters, and their connections in a text-based format in the clipboard.

app/common/xmlutils.cpp

@@ -0,0 +1,37 @@
+#include "xmlutils.h"
+
+#include "node/factory.h"
+
+Node* XMLLoadNode(QXmlStreamReader* reader) {
+  QString node_id;
+
+  XMLAttributeLoop(reader, attr) {
+    if (attr.name() == "id") {
+      node_id = attr.value().toString();
+
+      // Currently the only thing we need
+      break;
+    }
+  }
+
+  if (node_id.isEmpty()) {
+    qWarning() << "Found node with no ID";
+    return nullptr;
+  }
+
+  Node* node = NodeFactory::CreateFromID(node_id);
+
+  if (!node) {
+    qWarning() << "Failed to load" << node_id << "- no node with that ID is installed";
+  }
+
+  return node;
+}
+
+void XMLConnectNodes(const QHash<quintptr, NodeOutput*>& output_ptrs, const QList<NodeParam::SerializedConnection>& desired_connections)
+{
+  foreach (const NodeParam::SerializedConnection& con, desired_connections) {
+    NodeParam::ConnectEdge(output_ptrs.value(con.output),
+                           con.input);
+  }
+}