Add HGMD at the gene level

[mitalia]

While we're working to get HGMD linkages completed through the HGVS nomenclature work, we should provide end-users with a list of variants at the gene level that are in HGMD. Similar to how we have broken apart phenotypes into gene-level phenotypes and variant-level, HGMD mutations should also be listed to avoid missing anything. This requires a secondary mapping be created so that users can also filter by this (I.e. instead of things just being "in hgmd", they can filter by "variant in HGMD" and "gene in HGMD")