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/timelinewidget/view/timelineview.cpp

@@ -33,6 +33,8 @@
 #include "node/input/media/media.h"
 #include "project/item/footage/footage.h"
 
+OLIVE_NAMESPACE_ENTER
+
 TimelineView::TimelineView(Qt::Alignment vertical_alignment, QWidget *parent) :
   TimelineViewBase(parent),
   connected_track_list_(nullptr)
@@ -354,3 +356,5 @@ void TimelineView::UserSetTime(const int64_t &time)
   SetTime(time);
   emit TimeChanged(time);
 }
+
+OLIVE_NAMESPACE_EXIT