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.cpp

@@ -34,6 +34,8 @@
 #include "render/pixelformat.h"
 #include "videorenderworker.h"
 
+OLIVE_NAMESPACE_ENTER
+
 VideoRenderBackend::VideoRenderBackend(QObject *parent) :
   RenderBackend(parent),
   operating_mode_(VideoRenderWorker::kHashRenderCache),
@@ -382,3 +384,5 @@ void VideoRenderBackend::Requeue()
 
   CacheNext();
 }
+
+OLIVE_NAMESPACE_EXIT