go fmt
Server revocation support.
Change the dev server id.

I lost the key to the old one.
Further revocation work.

(snapshot for backup purposes.)
revocation tests pass
go fmt
Merge branch 'revocation'

This adds revocation support to the client and server.

Clients are able to generate revocation updates for their group
public key. They can upload this to their server and their server can
update its copy of the group public key so that exactly one contact no
longer has a valid member key. All, non-revoked contacts need to update
their member keys and so the server will distribute the revocation
update to them whenever anyone attempts a delivery with an old
generation number.

(It's not possible for the server to process a revocation update without
all the member keys being updated too because that would imply that the
server can now identity all previous messages sent by the revoked
contact.)