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/node/node.h

@@ -36,6 +36,8 @@
 #include "node/value.h"
 #include "render/audioparams.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief A single processing unit that can be connected with others to create intricate processing systems
  *
@@ -460,4 +462,6 @@ T* Node::FindOutputNode()
   return static_cast<T*>(FindOutputNodeInternal<T>(this));
 }
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // NODE_H