Add security manager configuration for EAP7 deployable

In eap6 deployable package, user can choose to start the BxMS in security mode.
eg: ./standalone-secure.sh
For EAP7 deployable package, we would give user option to enable the security manger as well.
Based on the discussion in PM maillist, we decide to add comments into standalone.xml and Add docmentation sessions to guide user to enable the security manager by docs.

So two changes are involved:
1) to add configurations for security manager for standalone*.xml
2) Add docs for this feature for EAP7 which another seperate BXMSDOC ( https://issues.jboss.org/browse/BXMSDOC-838 ) will track this.