Adapt Indico to the new RAVEM API

[pferreir]

Indico uses RAVEM in order to communicate with the audiovisual equipment that is installed in several rooms across CERN. It uses it specifically to connect a physical room to a Vidyo room.
Right now, RAVEM is used to check whether a room is connected (status) and to disconnect it from an already ongoing videoconferencing session: connection between rooms and Vidyo calls are requested directly to Vidyo. However, the latest version of the RAVEM API handles both connections and disconnections, thus making it more transparent for Indico and delegating the responsibility of taking care of the connection details on RAVEM.

The objective is, of course, to adapt Indico to the new RAVEM API. João and Aleksi should be the contact persons when it comes to information about the new API.

[jdafflon]

Fix: ​https://github.com/jacquesd/indico/commit/5382c79fba3c66f7f314dbb5d84fa48a58f32c71
And have a look at the cleaned-up version as well: ​https://github.com/jacquesd/indico/commit/6e4ef8d47fc7f4e05e31c2a6fcb5b2c3ac0676ae

[jmonnich]

Rebased branch: ​https://github.com/jacquesd/indico/commits/1591-fix-RAVEM-API-Update