sequence/feature design without a specified backbone

[jjti]

allow users to design a vector and match any backbone in the databases. insert specific, backbone agnostic

[jjti]

Could do this by putting in a mock backbone (random 3kbp sequence). It will be synthesized. then check the first and last fragment of each assembly (before filling) and see whether either is part of a vector in their database/match. If they are, use that backbone (extend that first/last frag), remove the random sequence, and fill

note: this probably won't always lead to the best solutions