feat: implement UI for logging out (#638)

* feat: implement UI for logging out

* feat: use old style dialogs for logout confirmation

* feat: implement manage sessions

* feat: implement session logout success dialog

* feat: use snjs alert for revoking sessions confirmation

* fix: make OtherSessionsLogout easier to read

app/assets/javascripts/preferences/components/PreferencesSegment.tsx

@@ -0,0 +1,5 @@
+import { FunctionComponent } from 'preact';
+
+export const PreferencesSegment: FunctionComponent = ({ children }) => (
+  <div className="flex flex-col">{children}</div>
+);