Option for default presentations

[paul1278]

Description

This pull request adds the option to supply default presentations on the create-call. This is a good addition to the default params / override options.

When submitting a POST-request as create-call, the supplied body will be used. If there is no body supplied or it is initially a GET-request, the default presentations will be added.

Testing Steps

Set the following inside your environment:

DEFAULT_PRESENTATIONS: "https://test.bigbluebutton.org/default.pdf->default_1.pdf,https://test.bigbluebutton.org/default.pdf->default_2.pdf"

This will download the default BBB-presentation two times, with two different names to showcase the options.
-> is the separator of URL and name because this is unlikely to appear inside an URL. Also with that, it is possible to add base64-presentations in the future.

[paul1278]

If you want anything changed please let me know

[pielonet]

Hi,

Thanks for this PR that we have been waiting a long time for.
Please release a beta version we can test soon.

[krim404]

i would like to push this pull request, as this feature would help us a lot and we would love to see it merged in the official branch.