Support à la carte dependencies

scraperlib grew significantly over the years, with modules very useful even beyond pure scraper usages. The ZIM wrapper is very useful in itself to name only one.

We are also considering addition of the currently separate kiwixstorage module, or the Kiwix catalog reader.

To support this Kiwix Swiss-army knife layout, we'd need to be able to install only some of the dependencies.

Dependencies would thus be organized into extra groups (ZIM, image, video, etc) with an all group that installs everything of course.

In addition, we could maybe had a try block on imports in each module to print a user-actionable message when importing code for which dependencies are not installed.

首先检查项目的依赖配置，以及 issue 中提到的模块导入。确定应如何组织 ZIM、image 和 video extras，包括 all 组，并判断缺少依赖的消息是否属于范围。选定的 extras 能够独立安装，并且涵盖约定的导入行为，即表示完成。