Add arrayutils.{to,from}Base64

Saves having to figure out which of atob/btoa is the right one.
Eradicate bogus byte strings from storage and API

It's just confusing. Use base64 for everything. This will break all
users of the API, but I haven't guaranteed stability yet. Add migration
code for anyone currently logged in via Webathena though.
Update zwrite-js for all the new APIs

Also make it use symlinks like remctl.