use completing-read instead of ido-specific alternative

[0fiscalentropy]

If you, for instance, prefer ivy, it will be used instead of ido

[atgreen]

Thanks for your patch.

I don't use ivy or ido globally, but I like ido here. How should we handle that?

[snuffop]

I would have to dig but an Idea would be test for IDO
or a var one could set.