Add a skeleton security policy.

For now this just allows everything (including replacing the
SecurityManager/Policy...) but we can start restricting things
later.

Change-Id: I3627bf06bd35fcebfb42bdc563617b830a999aaa
Reviewed-on: http://gerrit.dmdirc.com/3567
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>