api: add ability to create complete LSAT instance programtically

[Roasbeef]

A recent request from a develooper: they're using LSAT, but want to hand out "freebie" tokens to users to be able to play with. The first half here is being able to create the token itself (so just add+settle the invoice, them make an LSAT from that). The second half (with the larger design space), is how that token is actually imported into some application/CLI/service.