More appropriate permissions

Currently, the permission "administer filters" is used for access check on the admin page. As quotes contain, but are not (only) a simple filter, I would suggest to replace/extend this check with a permission like "administer quotes".

(This is also because I am just developing some extensions for your module which partially add directly to quote related settings and definitely are not primarily about filtering, but I do not find it appropriate to create a separate permission for a sub module.)