make configuration tree for directives reusable
make configuration tree for directives reusable

In a next step I want to add two config subtrees to define
directives to report and to enforce, see #31

stof/NelmioSecurityBundle,lyrixx/NelmioSecurityBundle,nelmio/NelmioSecurityBundle,romainneutron/NelmioSecurityBundle,romainneutron/NelmioSecurityBundle