conf: Split virDomainObjList into a separate file
    
    Our domain_conf.* files are big enough. Not only they contain XML
    parsing code, but they served as a storage of all functions whose
    name is virDomain prefixed. This is just wrong as it gathers not
    related functions (and modules) into one big file which is then
    harder to maintain. Split virDomainObjList module into a separate
    file called virdomainobjlist.[ch].
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>