Server/GFF/DAS.pm: &Bio::EnsEMBL::Slice::get_all_features_via_DAS: remove unused support for "--JOIN--" in "grouplabel" parameters.
(cherry picked from commit d7e4355e4df90209dbe28c502cdcd8de6c68e15e)
Server/GFF/DAS.pm: split "grouplabel" values with "/" instead of "--THEN--".
(cherry picked from commit fa86c2b26090a8e7476db69720b53c3875f677e8)
Server/GFF/DAS.pm: filter with a simple type_id contraint instead of sieves.
(cherry picked from commit 2a1da6b5908fd1ad3ebec1778ad5b685ebbd9e83)