Feat default presentation

[SpechtD]

Frontend works so far.
Backend is not yet functional.

[pielonet]

Hi,

From BBB 2.7.2 on it is now possible to add a default presentation URL as a single create call query string parameter :
See : https://docs.bigbluebutton.org/development/api/#create

preUploadedPresentation	String	If passed with a valid presentation file url, this presentation will override the default presentation. To only upload but not set as default, also pass preUploadedPresentationOverrideDefault=false (added 2.7.2)

This can be used to upload a single file default presentation.

Kind regards,
Thierry