[reSIProcate] moving libb2bua out of the main repository

[Daniel Pocock]

I'm moving the B2BUA project out of the main repository, it will either
go to another part of the SVN repository or into a standalone git repository

b2bua will remain in the 1.8 branch but will not be part of any 1.9 or
later release

As the code is not being actively maintained, there is no guarantee that
the b2bua code will be updated to work with future reSIProcate releases,
however, it should continue to work with those releases it has worked
with in the past.