Add getUserAddress to HackSessionContext
Remove getAddress function (superceeded by getPublicId for now)
Always make the grain's address be the `from` in the smtp envelope.

Also remove old logic for replacing `from` header in messages, and
instead allow either the grain's address or the user's sandstorm
registered address to be used.
Show sign-in arrow on invite acceptance.
Update Hacker CMS link.
Fix typo in readAll function
Merge pull request #27 from jparyani/fix-readall-typo

Fix typo in readAll function
Complain and stop updates if system is not ready for unprivileged UID namespaces.
Merge branch 'master' of github.com:kentonv/sandstorm
Merge pull request #26 from jparyani/mail-fix-from

Allow sandstorm registered email addresses in outgoing mail
Add FileSaver library
Add basic working version of backup/restore
Add fs-extra package
Add GrainInfo struct to grain.capnp and persist it through backup.

Backup also includes log now, although it isn't used in restore.
GrainInfo is encoded and is named metadata in the archive. The sandbox's
data now all goes into a folder called data.
Change restore to be a global function. Also add icon for download