OpenVidu: Prevent redundant connections when clicking Join button multiple times
Summary: We disable the button while doing the request, and make sure redundant tokens are ignored
Test Plan: ./phpunit
Reviewers: #hkccp_developers, vanmeeuwen
Reviewed By: #hkccp_developers, vanmeeuwen
Subscribers: #hkccp_developers
Differential Revision: https://git.kolab.org/D2008