Create translation managing site

**Is your feature request related to a problem? Please describe.**

It's currently not easy to create and maintain ZeroNet translation because all translation happens just in files so it's hard to track all changes.

**Describe the solution you'd like**

Create a translation/localisation platform as ZeroNet zite. It should be similar to Transifex, Crowdin or other existing platforms. It should be possible to track all changes to the original words, translated words, missing translations... It should also be possible to automatically merge and pull all changes to/from GitHub (or Git Center).

Also, that zite should be open to anyone to host and translate own projects. Something like Git Center which allows hosting Git projects as merged sites. So there would be the main UI for translation, but each project would have a separate merged site for storing data.

**Describe alternatives you've considered**

Until you finish translation zite, you should use some other translation/localisation platform, such as Transifex or Crowdin.

该 issue 没有指定文件、测试或入口点。首先将所请求的翻译跟踪、GitHub/Git Center 同步以及按项目托管转化为一份达成共识的设计；要视为完成，必须定义范围和实现计划。

由索引模型根据 Issue 内容生成。