Allow custom junction boundary definitions in MakeDb

[Jason Vander Heiden]

We could use an argument in MakeDb-igblast to allow for custom junction boundaries in IMGT gapped references, as they apparently differ in some cases. Eg, IGL of rhesus macaques:

IGH & IGK
FR1-IMGT CDR1-IMGT FR2-IMGT CDR2-IMGT FR3-IMGT
(1-26) (27-38) (39-55) (56-65) (66-104)

IGL
FR1-IMGT CDR1-IMGT FR2-IMGT CDR2-IMGT FR3-IMGT
(1-27) (28-39) (40-58) (59-68) (69-107)

See #150 for more details.

Maybe as an optional yaml file of boundaries, similar conceptually to `shazam::RegionDefinition`?

[Jason Vander Heiden]

Done in cba7a41.