Add Session to Messenger

Session Messenger is a messenger that tries to combine the usability of Signal with the security of Briar by utilizing Oxen Service Nodes (which are FOSS), the nodes of the Lokinet onion router. The desktop and mobile apps are FOSS forks from their Signal counterparts, their e2ee is based on the Signal Protocol; they call it the Session Protocol. It also supports open groups, which require the operator hosting of a open group server, which is also FOSS. A/V Calling is in the works. There is also a research paper available that describes Session. By default it uses Google Push Services to wake up when a message arrives (the message is then pulled from a service node), but that can be turned off, so it uses regular polling (every hour or so). The service nodes cache your messages when you are offline for up to 14 days. Sent files are stored end2end encrypted on a central server for 14 days run by OPTF which is a registered charity in Australia. This may change in the future.