Rework avatars.

Now we have a concept of an avatar at the server, realm, and scene level
and we have the groundwork for a realm store. New uesrs no longer props,
they get a default avatar. New system supports gender
{male,female,neutral} and {child,adult}.

crates/chattyness-user-ui/src/components/hotkey_help.rs

@@ -50,6 +50,7 @@ pub fn HotkeyHelp(
                     <HotkeyRow key="i" description="Inventory" />
                     <HotkeyRow key="k" description="Keybindings" />
                     <HotkeyRow key="a" description="Avatar editor" />
+                    <HotkeyRow key="t" description="Avatar store" />
                     <HotkeyRow key="l" description="Message log" />
 
                     // Emotions