文本预览插件
插件安装、更新、删除详见 《安装、更新、删除插件》
文本预览插件支持预览的文件 MIME 类型包括：
- text/plain
- text/html
- text/css
- text/javascript
- text/x-c
- text/x-java-source
- text/markdown
- application/xhtml+xml
- application/xml
- application/javascript
- application/json
- application/x-sql
- application/x-php
- application/x-sh
- application/x-shellscript