This commit addresses Issues #4 and #7. See expanded commit message for details.

I have created a $Instance()->getId() method which will accept either a title or path and return an ID.

I have updated $rbac->Permissions->roles() and $rbac->Roles->Permissions:
    * They now use the new getId() method
    * If the second parameter is 'false' then an array is returned which includes the permission/role ID, Title and Description
    * I fixed a bug in the sql query. The 'Order By' clause was incorrect. See commit diff for details

I have created Unit Tests for all of the above.