global: session 2.0

• Upgrades session serialization to LZMA.

• Implements session signing. This avoids cache request for invalid sessions and reduces the DDoS attack surface.

• Removes IP address storage+checks. This avoids data privacy issues and enables users with multiple connections (e.g. WIFI+LTE, multiple WIFI connections on trains+stations) to stay signed in.

• INCOMPATIBLE Drops all active sessions during upgrade. Might result in log entries about non-restorable sessions.

Signed-off-by: Marco Neumann <marco@crepererum.net>