单文件上传，自动复制URL地址到剪贴板

[jahentao]

Fix: #195

每次写markdown，上传单个图片，要获取图片的URL，要经过“选中刚上传的图片”->“点击更多”->"获取地址"->“等待弹出窗口”->“点击复制地址”五个步骤，真的不胜其烦。

所以在单个上传成功后，自动复制文件路径到剪贴板要方便很多。

同时在设置项中，添加该项设置，考虑到其他用户的使用，默认禁用。

在Windows、Linux下测试通过。

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