Currently we are converting dir_info to/from lists all the time.
The reason is that dir_info is stored as list of dicts in *.dir files,
but that makes it hard to work with. In addition to that, we will likely
be changing .dir file format in the near future #829, so we need to
abstract away dir_info into something that we won't care how it will be
stored on disk.
Related #3256
Related #4847
