Decrease maximum number of search suggestions.

This fixes an issue with the menu going below the bottom of screen
with non-tiny windows, and it was rare that anyone benefitted from the
extra suggestions.

Fixes: #4133.

static/js/search.js

@@ -53,7 +53,7 @@ exports.initialize = function () {
             return suggestions.strings;
         },
         fixed: true,
-        items: 30,
+        items: 12,
         helpOnEmptyStrings: true,
         naturalSearch: true,
         highlighter: function (item) {