FTP backend

[berl]

The BICCN is storing image data at the Brain Image Library and BIL's current approaches for raw image data access are

• anonymous FTP for public access once image data has been published
• authenticated methods with shell access for users for in-process/unpublished data

An anonymous FTP backend for slicedimage would allow users to load published BIL data locally and some authenticated method would allow the same kind of access for unpublished data on BIL.

@ttung per our slack conversation and @ambrosejcarr just in case you're interested