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/dialog/task/task.cpp

@@ -1,8 +1,30 @@
+/***
+
+  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 "task.h"
 
 #include <QMessageBox>
 #include <QThread>
 
+OLIVE_NAMESPACE_ENTER
+
 TaskDialog::TaskDialog(Task* task, const QString& title, QWidget *parent) :
   ProgressDialog(task->GetTitle(), title, parent),
   task_(task),
@@ -69,3 +91,5 @@ void TaskDialog::TaskFailed(const QString &s)
   task_failed_ = true;
   task_error_ = s;
 }
+
+OLIVE_NAMESPACE_EXIT