Support iPuz diagramless puzzles

[boisvert42]

I think this would be pretty easy -- it's just adding the "diagramless" puzzleKind and mapping it to whatever you do for diagramless puz files.

[boisvert42]

There's no official equivalent for JPZ but that probably shouldn't stop us from making one if we want.

[jpd236]

I think it's already done:

https://github.com/mrichards42/xword/blob/master/puz/formats/ipuz/load_ipuz.cpp#L186

[boisvert42]

Yes, my mistake! Carry on