Unlock is quite heavy in terms of I/O and thus waiting time, so we (in datalad) probably should provide also a progress bar indicator.

1. how could I obtain a list of files which would be unlocked given a set of paths?

2. could there be a --json mode of output (consistent with add --json etc)?

[[!meta author=yoh]]
[[!tag projects/datalad]]

> added --json option [[done]] --[[Joey]]
