various: encapsulate all code in the olive namespace to avoid name collisions

Large-scale code cleanup. Also adds a license to the top of all files that were
missing it.

app/widget/nodeview/nodeviewitemwidgetproxy.h

@@ -1,3 +1,23 @@
+/***
+
+  Olive - Non-Linear Video Editor
+  Copyright (C) 2019 Olive Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
 #ifndef NODEVIEWITEMWIDGETPROXY_H
 #define NODEVIEWITEMWIDGETPROXY_H
 
@@ -14,7 +34,7 @@ class NodeViewItemWidget : public QWidget {
   Q_PROPERTY(QColor titlebarColor READ TitleBarColor WRITE SetTitleBarColor DESIGNABLE true)
   Q_PROPERTY(QColor borderColor READ BorderColor WRITE SetBorderColor DESIGNABLE true)
 public:
-  NodeViewItemWidget();
+  NodeViewItemWidget() = default;
 
   QColor TitleBarColor();
   void SetTitleBarColor(QColor color);