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/clickablelabel/clickablelabel.cpp

@@ -1,5 +1,27 @@
+/***
+
+  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/>.
+
+***/
+
 #include "clickablelabel.h"
 
+OLIVE_NAMESPACE_ENTER
+
 ClickableLabel::ClickableLabel(const QString &text, QWidget *parent) :
   QLabel(text, parent)
 {
@@ -21,3 +43,5 @@ void ClickableLabel::mouseDoubleClickEvent(QMouseEvent *)
 {
   emit MouseDoubleClicked();
 }
+
+OLIVE_NAMESPACE_EXIT