Currently namespace name and path have uniq validaiton which does not
allow us to use same group name/path inside different groups. This
commit changes validation in next way:
* Allow same namespace name with different parent_id
* Allow same namespace path. Uniq validation should be handled by routes table
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
