Fix dependencies in bellbot code

[cdondrup]

The missing dependencies have to be added and the unnecessary ones have to be removed, e.g.:

CMake Warning at /home/cdondrup/ros_ws/build/strands_hri/bellbot_gui/cmake/bellbot_gui-genmsg.cmake:3 (message):
  Invoking generate_messages() without having added any message or service
  file before.

  You should either add add_message_files() and/or add_service_files() calls
  or remove the invocation of generate_messages().
Call Stack (most recent call first):
  /opt/ros/indigo/share/genmsg/cmake/genmsg-extras.cmake:304 (include)
  strands_hri/bellbot_gui/CMakeLists.txt:77 (generate_messages)


-- bellbot_gui: 0 messages, 0 services