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/render/backend/videorenderbackend.h

@@ -31,6 +31,8 @@
 #include "videorenderframecache.h"
 #include "videorenderworker.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief A multithreaded OpenGL based renderer for node systems
  */
@@ -139,4 +141,6 @@ private slots:
 
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // VIDEORENDERERBACKEND_H