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/toolbar/toolbarbutton.cpp

@@ -20,6 +20,8 @@
 
 #include "toolbarbutton.h"
 
+OLIVE_NAMESPACE_ENTER
+
 ToolbarButton::ToolbarButton(QWidget *parent, const Tool::Item &tool) :
   QPushButton(parent),
   tool_(tool)
@@ -31,3 +33,5 @@ const Tool::Item &ToolbarButton::tool()
 {
   return tool_;
 }
+
+OLIVE_NAMESPACE_EXIT