Updated permission structure

1. Permissions are no longer based on the \Oonix\MongoMongoDB object as all collections are part of a DB, hence the permission path for the DB is a parent of the collection
2. \Oonix\Mongo\MongoCollection no longer extends \MongoCollection but rather wraps it and exposes all methods with __call(), performing RBAC as required
3. \Oonic\Mongo\MongoClient now has 3 prepended arguments, the 3rd being an optional callback to provide custom RBAC permission paths