Bugfix: Nested DeepL commands keep the page of a running translation 

Description 

The DataHandler command deepltranslate remembers the record it translates for the whole request. The site, the page, the glossary and the translation context of every translated field are taken from that record. A deepltranslate command issued while another record is still being localized replaced it for the rest of that localization. web-vision/deepltranslate-auto-renew issues such commands from its DataHandler hooks.

The remaining fields of the running localization were then translated with the site, the glossary and the translation context of the other record, and its page was marked as translated with DeepL. With the other record on a site without the target language, the rest of the localization failed.

Impact 

A deepltranslate command issued within another one restores the record of the running command when it is done. A command issued on its own keeps its record for the rest of the request, as before.

See pull request #696.