Fix ZRTP 'version' byte and superfluous null bytes.

1) The wrong bit was set in the 'version' byte (0x20 instead of 0x10).

2) Each handshake packet included 12 extra null bytes in between the ZRTP header
   and the ZRTP 'message'.  These don't cause any problems or have any security
   implications, but it's definitely incorrect.  In order not to break backwards
   compatibility, we have to intentionally do the wrong thing when it looks like
   we're talking with old clients.

   The initiator indicates that it's a "new" client by setting a version of 1 in the
   initiate signal.  The responder indicates that it's a "new" client by either setting
   the "new/correct" version byte (0x10) on the handshake packets it sends, or the
   old/incorrect" version byte (0x20).

  This is a complete mess and it fucks up most of the handshake packet code.
  Eventually we'll phase this out.
Handle dropped ConfAck and format SRTP packets more appropriately

1) If an Initiator is waiting for a ConfAck packet and gets
   something that looks like an RTP packet instead, we assume
   the ConfAck packet as dropped and continue.

2) Set the version bits and timestamp on SRTP packets.
Gradle 1.9, android plugin 0.7.+