Have a user-friendly project inventory

## Feature

Right now the only way to see projects on Code.mil is to look at the `code.json` file. I would like to have a user-friendly view of the projects in that inventory for anyone to peruse. The Code.gov team [has something like this](https://code.gov/#!/browse-projects), but I'm not sure if it is reusable, and we don't necessarily need it to look like that.

首先查看现有的 code.json 清单以及 issue 中链接的 Code.gov browse-projects 示例。定义一个便于用户浏览项目的视图，包括其范围和呈现方式，并考虑所引用的 Code.gov 方法是否可以复用；当用户无需打开 code.json 就能浏览清单时，即视为完成。

由索引模型根据 Issue 内容生成。