Add CDR3 and FRW4 to extractVRegion

[Jason Vander Heiden]

Should include extraction of CDR3 and FWR4, which will require input of junction lengths. May also be worth adding a small wrapper that takes in a data.frame with column names and returns an updated data.frame, as this is the usual use case.

[Jason Vander Heiden]

I don't think we actually need this anymore now that we usually output it from MakeDb.