Bug 28519: Put CGI::Session::Serialize::yamlxs in lib directory

Bug 28519: Put CGI::Session::Serialize::yamlxs in lib directory

This patch adds a "lib" directory to the source tree which gets
mapped to the same directory as "C4" and "Koha" for single and
standard installations.

CGI::Session::Serialize::yamlxs is put into this "lib" directory.

This patch also includes some changes so that dev/git installations
work as well.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>