Update to the latest version of codec2, and add support for all bit rates

The version of codec2 that ships with GNU Radio is obsolete, and doesn't interoperate with current versions of codec2.  In this patch, I have pulled in the latest version of codec2, updated the GNU Radio blocks to use its new API, added support for all six bit rates, and updated the QA code, sample code and GRC files to match.  I've verified that all six bit rates appear to work correctly.