<install-scripts> Add CONF_BROKER_SESSION_SECRET and randomize if absent
Adding session secret for console

Added very minimal documentation of the CONF_BROKER_SESSION_SECRET,
CONF_CONSOLE_SESSION_SECRET, and CONF_BROKER_AUTH_SALT parameters.
Merge pull request #19 from themurph/session_secret

<install-scripts> Add CONF_BROKER_SESSION_SECRET and randomize if absent