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/pixelformat.cpp

@@ -28,6 +28,8 @@
 #include "common/define.h"
 #include "core.h"
 
+OLIVE_NAMESPACE_ENTER
+
 bool PixelFormat::FormatHasAlphaChannel(const PixelFormat::Format &format)
 {
   switch (format) {
@@ -230,3 +232,4 @@ FramePtr PixelFormat::ConvertPixelFormat(FramePtr frame, const PixelFormat::Form
   }
 }
 
+OLIVE_NAMESPACE_EXIT