Implement a method in TorrentManger to write a Data packet of a torrent to the correct location on
disk. Also create a utility method to initialize the structure for fileState, fixing a bug of
opening a non-existent file with the fs::stream::in bit.

Change-Id: Ife08c2fef93d6a6cba906c3735ffac57506b7750
diff --git a/src/torrent-manager.hpp b/src/torrent-manager.hpp
index 3c4b923..ca83a2b 100644
--- a/src/torrent-manager.hpp
+++ b/src/torrent-manager.hpp
@@ -92,6 +92,11 @@
   // Seed the specified 'data' to the network.
 
  protected:
+  bool writeData(const Data& packet);
+  // Write the Data packet to disk, return 'true' if data successfully written to disk 'false'
+  // otherwise. Behavior is undefined unless the corresponding file manifest has already been
+  // downloaded.
+
   void onDataReceived(const Data& data);
 
   void onInterestReceived(const Name& name);