Unify avatar class generation

src/views/renderutils.nim

@@ -88,3 +88,9 @@ proc getTabClass*(query: Query; tab: QueryKind): string =
   result = "tab-item"
   if query.kind == tab:
     result &= " active"
+
+proc getAvatarClass*(prefs: Prefs): string =
+  if prefs.squareAvatars:
+    "avatar"
+  else:
+    "avatar round"