Move BankType from RawBank to dedicated namespace

required so that Allen can use RawBank::BankType without including RawBank.h (which pulls in more things that should not be included) -- see Allen!2143 (merged) (which is separate from this MR)

must be applied:

1. after (or in conjunction with) Lbcom!880 (merged), Rec!4592 (merged), Boole!754 (merged), Allen!2146 (merged) and MooreOnline!665 (merged) (ie. those 5 can be merged independently of this one, and of each other)
2. in conjunction with Moore!5292 (merged).