Rename corba servers

  With the increasing number of corba server, it is necessary to reorganize
  the server names in the naming service:
    - hpp.corbaserver/basic.obstacle
    - hpp.corbaserver/basic.problem
    - hpp.corbaserver/basic.robot
Reorganize idl interfaces

  - interfaces Obstacle, Problem and robot are now embedded into module
    hpp::corbaserver for more consistency and extendability.