mkprof command doesn't write empty tables

[goodmami]

The mkprof subcommand of the delphin command is meant to replicate art's behavior, but currently empty table are not written. The --full option could be used for copying non-empty profiles, but there's no way to write the empty tables like art does.

Proposal: add a --skeleton option for the current behavior (only item and relations are written), and the default behavior writes all tables define in Relations, even if empty.