reduce sidecar size by default

[mgxd]

Essentially mimic use of the --minmeta flag, but allow users the option to extract more/all DICOM metadata (--all-meta?).

This will greatly reduce conversion output directory sizes by default, especially for longer protocols.

[yarikoptic]

Probably you are observing big sizes on dicoms from some scanners for which we didn't kill their custom manufacture specific fields? Some examples could come handy