huge rewrite of ui-server

Update to use the new read/write token for posting and receiving data
from "channels", which defeats spam and is a solution for the chicken
and egg problem of negotiating an intermediary data source

Also makes most database fields bytea where possible

Improved function for decrypting content

Clearer separation of fetching data updates vs. showing list of posts.

Improvements to key management code

Misc changes

Note: still requires tidying, bug fixes, deduplication etc.