SSH support, websocket buffer, session sharing (read-only), etc.

• Resynced FreeRDP (FQDN hotfix, introduced into myrtille 1.7.0, is still active... wfreerdp need some love :/)
• the RDP security protocol (NLA, TLS, RDP, etc.) can now be selected from the login screen (RDP for compatibility and interactive logon, or in case of NLA issue; see #116)
• SSH terminal support (thanks Paul)
• removed any RDP references on the gateway to make it fully protocol agnostic (support of any remote access protocol)
• file transfer and print download can now be disabled from web config (along with remote clipboard and session sharing)
• when sharing a remote session, guests now can't interact with it (they are just spectators)
• included prompt for user credentials in enterprise mode
• fixed login failure when passing domain in enterprise mode if IP is used instead of FQDN
• fixed some css in enterprise mode (under Firefox)
• websockets are now buffered for optimal performance on high latency / low bandwidth networks (thanks SieldP)
• re-enabled stat button, which could help to diagnose connection issues (shows latency, bandwidth usage, etc.)
• added a small icon on top of the screen to toggle the toolbar while connected (thanks windylea)
• improved error messages in case of connection failure
• some refactoring