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/codec/ffmpeg/ffmpegdecoder.h

@@ -37,6 +37,8 @@ extern "C" {
 #include "ffmpegframecache.h"
 #include "project/item/footage/videostream.h"
 
+OLIVE_NAMESPACE_ENTER
+
 /**
  * @brief A Decoder derivative that wraps FFmpeg functions as on Olive decoder
  */
@@ -134,4 +136,6 @@ private slots:
 
 };
 
+OLIVE_NAMESPACE_EXIT
+
 #endif // FFMPEGDECODER_H