Restructuring ZRTP code as own library - plase disable ZRTP support until restructuring is ready

[Werner Dittmann]

All,

as proposed by Eric and due to some other reasons I'm restructuring the
ZRTP code into an own library. Thus ZRTP will live in its own directory
parallel to the other lib directories. This restructuring process is
ongoing and is not yet finished - thus please disable ZRTP support
during your builds for the next days.

In addition to the restructuring I'm also enhancing ZRTP to work with
Zfone-Beta2. This new Beta2 introduced some changes to the ZRTP protocol.
I need to do some more tests with Zfone-Beta2.

Also note that ZRTP uses GPL now. ZRTP is an optional feature for
minisip and is not required to build a generic VoIP client as this is
the matter of the other libm* modules. Thus it's GPL now.

Thanks for your understanding and patience.

Regards,
Werner