Add filters for search

Would be awesome to allow the user to filter for `Best Match` `Most Stars` etc... for repository search and the same for users (`Most Followers`, etc...).

Will need to do the same for issue search when that gets added in to the app as well #12.

Issue 中没有指出任何文件、测试或入口点。首先定位仓库搜索和用户搜索界面，以及它们现有的结果加载路径；当用户可以选择所要求的仓库和用户排序筛选条件时，即视为完成，问题搜索筛选条件则推迟到问题搜索存在之后再处理。

由索引模型根据 Issue 内容生成。