Start writing role to database (#3120)

Scaffolding for guest members in channels

Release notes:
- You can now set channels to "public" which will allow anyone to join
and become a member. In a future release guests joining public channels
will have reduced permissions.

crates/theme/src/theme.rs

@@ -286,6 +286,8 @@ pub struct TabbedModal {
     pub header: ContainerStyle,
     pub body: ContainerStyle,
     pub title: ContainedText,
+    pub visibility_toggle: Interactive<ContainedText>,
+    pub channel_link: Interactive<ContainedText>,
     pub picker: Picker,
     pub max_height: f32,
     pub max_width: f32,