Add "multi-omics" column

[DeniseSl22]

Based on a project I'm working on (together with @dygdedesener and @susancoort), it would be great to have one column with unified IDs for both GeneProducts/Proteins and Metabolites. Since we now have one column with Ensembl IDs, and one with ChEBIs, I would propose to create on column where these are merged (there should not be any overlap between these two databases). The users can sue this column as a key, when adding for example log2FC data from both transcriptomics and metabolomics measurements in one go, and then later apply the same visualization for all DataNodes.