Use crowdin-cli for crowdin API usage

Tooling at https://github.com/nuxeo/tools-nuxeo-crowdin/ defines a crowdin_update.py file to retrieve/push files to Crowdin.
But the crowdin-cli tool actually provides a python version at https://github.com/PaulGregor/crowdin-cli (here's a java version too), it could be useful to reuse this module (and beenfit from the credentials management to keep the API key secret)