This commit adds a new config setting:
```toml
disableLanguages = ["fr"]
```
If this is a multilingual site:
* No site for the French language will be created
* French content pages will be ignored/not read
* The French language configuration (menus etc.) will also be ignored
This makes it possible to start translating new languages and turn it on when you're happy etc.
Fixes#4297Fixed#4329