Allow setting the text of a config.xml for setConfigXML

Updated bigbluebutton-api-js to 9bb6b9fdd2fb.
Had to adapt the calls to bigbluebutton-api-js that have changed.

Note: For now the config.xml content is passed in the URL when setConfigXML
is called and not in the body of the POST call. This has to be double checked.

refs #1110
Ignore .nvmrc
Signal setting data for config.xml as experimental

Not thoroughly tested yet, might still have some issues.

refs #1110