Notifications center/Web client

From Nasqueron Agora

The Notifications center web client is under development with two components:

 * a SSE server, https://devcentral.nasqueron.org/D2718
 * a JS client to read them and show them on https://infra.nasqueron.org

For more information, you can discuss the proof of concept on https://devcentral.nasqueron.org/T1682.