add appropriate publisher information when pushing to figshare

[cboettig]

• Could add figshare as a <publisher> node when using eml_figshare
• Should re-use a general-purpose function for adding publisher to data
• Should check that publisher node isn't already set to avoid duplicating entries.

[cboettig]

eml_figshare() publishing now deprecated. Researchers can easily deposit EML metadata on figshare (with rfigshare or the web interface), but the EML will always be more valuable on a metacat repo that can actually allow repository users to query metadata embedded in the eml.