IDMapper for mirbase, to map between mature<->immature miRNA

[martijn]

Request for an IDMapper for mirbase.

This is in particularly useful because Current ensembl based Derby databases do not contain mappings to mature miRNA.

Ensembl does map to immature miRNA's, because they are bound to a chromosome location. However, there is a many-to-many relation to mature miRNA's. An immature miRNA can give rise to a sense or antisense mature miRNA, and also different immature miRNA's can give rise to the exact same mature miRNA.

Example: symbol: hsa-miR-155 immature: Mirbase MI0000681, gelinkt aan ENSG00000207795 mature: mirbase MIMAT0000646

Another example: symbol: hsa-let-7a has 3 ensembl ids