add demo for multiband CSP
add demo for multiband CSP

drsternburg/bbci_public,svendaehne/bbci_public,IrinaNicolae/bbci_public,bbci/bbci_public,drsternburg/bbci_public,svendaehne/bbci_public,bbci/bbci_public,svendaehne/bbci_public,IrinaNicolae/bbci_public,drsternburg/bbci_public,bbci/bbci_public,IrinaNicolae/bbci_public