Log Message:
snac: update to 2.73. Changes:

Added support for customizing and translating the web UI language
via simple `.po` files. For more information on how to install
language files or create new ones, please see `snac(8)` (the
administrator manual).

New user support for blocking hashtags from the web UI.

The `Content-Security-Policy` HTTP header is now always sent to disable
any JavaScript, instead of just being suggested in the documentation.

Image attachments in SVG format are now disabled by default; you can
enable them back by setting the `enable_svg` value to `true` in
`server.json`.

Several fixes (contributed by inz).