began large scale restructure

app/widget/projectexplorer/projectexplorer.cpp

@@ -0,0 +1,17 @@
+#include "projectexplorer.h"
+
+ProjectExplorer::ProjectExplorer(QWidget *parent) :
+  QWidget(parent),
+  view_type_(TreeView)
+{
+}
+
+const ProjectExplorer::ViewType &ProjectExplorer::view_type()
+{
+  return view_type_;
+}
+
+void ProjectExplorer::set_view_type(const ProjectExplorer::ViewType &type)
+{
+  view_type_ = type;
+}