add a option to display theme selection or not

conststr.php

@@ -73,6 +73,7 @@ $constStr = [
             'diskname' => 'The disk name you want show.',
             'disktag' => 'A tag used in store config and url.',
             'disableShowThumb' => 'if 1, the ShowThumbnail button will not display',
+            'disableChangeTheme' => 'if 1, the Theme selection button will not display',
             'downloadencrypt' => '0 or 1. if 1, the files in encrypt folder can be downloaded without password',
             'background' => 'Set an url as background photo.',
             'theme' => 'Select theme.',
@@ -95,6 +96,7 @@ $constStr = [
             'diskname' => '这个盘你想显示什么名称。',
             'disktag' => '一个标签，用于保存配置，多盘时会显示在url中。',
             'disableShowThumb' => '如果填 1, ‘显示缩略’按钮将被隐藏。',
+            'disableChangeTheme' => '如果填 1, 主题选择切换将被隐藏',
             'downloadencrypt' => '0 或 1。如果 1, 那加密目录内的文件可以不需要密码就能下载。',
             'background' => '设置一个url作为背景。',
             'theme' => '选择一个主题。',