Provide pickers for the publication configuration

This issue regroups the different pickers requirements for the publication configuration.

1. Source page: propose only the book pages (not the content sub-pages, administration pages, ...) (see also BVERSION-96)
2. Destination space: see BVERSION-86
3. Version: only propose versions from the book (see BVERSION-22)
4. Variant: only propose variants from the book (see BVERSION-43). It should be greyed out if none exist.
5. Language: only propose language set in the book. It should be greyed out if none exist or if languages are not enabled in the Languages administration page