Dataset streaming

[zhiltsov-max]

Currently, Datumaro only works with static datasets on the disk. However, it can be useful to provide an ability to input dataset from the standard input, or devices (IP cameras etc.). Opposite, it can also be useful to allow printing dataset into the standard output (the format is same as datum filter --dry-run, but for other commands too). This can help to support The Unix Way and allow to integrate the tool well with different existing CLI tools.