add pbmc2_media_patient to omni_batch data

Small code changes from: https://renkulab.io/projects/supermegaiperste/cellmixs-data-csf-media-patient (particularly for the sce object to get "batch_id" and "cluster_id" infos)

Repo is at: https://renkulab.io/gitlab/omni_hackathon/omni_batch/cellmixs-data-pbmc2-media-patient-data

P.s. chose "media" as batch effect, but "patient" could be another option