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/index.ts

@@ -1,3 +1,5 @@
 export * from './Content';
 export * from './MenuItem';
 export * from './PreferencesPane';
+export * from './PreferencesGroup';
+export * from './PreferencesSegment';