Add basic implementation of the participants methods

[arnaud-jacquemin]

Hello,

Here is a basic implementation of the following methods :

• get_participant_properties
• invite_participants
• remind_participants

I don't have time to write unit tests, but I made several functional tests and everything works as intended.

Hope it helps !

[lindsay-stevens]

Thanks for the PR :thumbsup:. If you can add tests + implement all params for these new methods I'd be happy to merge :ok_hand: :100:.