Beginning of libtextsecure refactor.

1) Break out appropriate components.

2) Switch the incoming pipeline from SendReceiveService to
   the JobManager.

src/org/thoughtcrime/securesms/crypto/DecryptingPartInputStream.java

@@ -37,8 +37,6 @@ import javax.crypto.spec.SecretKeySpec;
 
 import android.util.Log;
 
-import org.whispersystems.textsecure.crypto.MasterSecret;
-
 /**
  * Class for streaming an encrypted MMS "part" off the disk.
  *