Option to export projects to Android and/or iOS

It would be really cool if students could generate links to install their projects as Android or iOS apps on a phone or tablet. The app would be a web view, wrapped as an application with a set of generated files.

Concerns:
- The set of available events would be much smaller. It may be that we should simplify the event model anyway to include just mouse moves, clicks, and drags.
- iOS might not be possible without the student either jailbreaking or getting a $100 developer license. Android would require enabling third-party apps.

首先定义项目生成的文件将如何支持为 Android 或 iOS 封装的 Web 视图，并审查 issue 中关于事件模型的问题。在实现之前明确平台、许可和安装方面的限制。完成的标准是学生能够为受支持的平台生成可安装的链接，并且精简后的事件集已得到清晰记录。

由索引模型根据 Issue 内容生成。