add access permissions

Issue Summary

hi.

Pegoeditor currently provides control over who can administer the module. it also needs to provide a permission to allow or disallow different rules from using the editor.

the administration interface does have a checkbox to allow future users to use the editor by default or not, but this has nothing to do with old users. so we can alternatively provide the same functionality for existing users. if we do, then the access permission will become unnecessary.