Event history: format script text and output correctly

This Fixes the Event History page for Remote Command actions:
 - Use `<pre>` instead of `<code>` to preserve line-endings
 - Use `StringEscapeUtils.escapeHtml` instead of `StringUtil.htmlifyText` to prevent XSS attacks

Before:
![previous version screenshot](https://cloud.githubusercontent.com/assets/250541/3037998/95529c84-e0c7-11e3-85c5-d2979744ac0a.png)

After:
![next version screenshot](https://cloud.githubusercontent.com/assets/250541/3038032/155a9b84-e0c8-11e3-9ac1-b0227d236376.png)