Allow adding multiple metadata files and representations via the CLI

[prettybits]

Currently the CLI only allows to add one metadata file and one representation (from one or more files and folders), it would be great to have the ability to specify multiple representations and multiple metadata files, including their respective types and/or IDs.

As well, currently the specified metadata file is assumed to be descriptive metadata and thus is added to dmdSec and put into metadata/descriptive, having the ability to specify whether a metadata source file contains descriptive or administrative (or more specifically preservation, rights, technical or "source") metadata would be great to have.