Investigate the feasibility of making icub-contrib-common a soft dependency

[Nicogene]

In the actual state without icub-contrib-common is not possible to compile icub-basic-demos.

Maybe with a little effort of refactoring of cmake is possible to at least make it a soft dependency

[Nicogene]

These are (hopefully) all the parts where icub-contrib-common is used:

$ git grep -i icubcontrib_
CMakeLists.txt:list(APPEND CMAKE_MODULE_PATH ${ICUBCONTRIB_MODULE_PATH})
CMakeLists.txt:icubcontrib_set_default_prefix()
CMakeLists.txt:icubcontrib_add_uninstall_target()
demoForceControl/CMakeLists.txt:                              ${ICUBCONTRIB_MODULE_PATH})
demoForceControl/CMakeLists.txt:icubcontrib_set_default_prefix()
demoForceControl/CMakeLists.txt:  icubcontrib_add_uninstall_target()
demoForceControl/CMakeLists.txt:yarp_install(FILES ${scripts} DESTINATION ${ICUBCONTRIB_APPLICATIONS_TEMPLATES_INSTALL_DIR})
demoForceImitation/CMakeLists.txt:                              ${ICUBCONTRIB_MODULE_PATH})
demoForceImitation/CMakeLists.txt:icubcontrib_set_default_prefix()
demoForceImitation/CMakeLists.txt:    icubcontrib_add_uninstall_target()
demoForceImitation/CMakeLists.txt:yarp_install(FILES ${scripts} DESTINATION ${ICUBCONTRIB_APPLICATIONS_TEMPLATES_INSTALL_DIR})
demoRedBall/CMakeLists.txt:                              ${ICUBCONTRIB_MODULE_PATH})
demoRedBall/CMakeLists.txt:icubcontrib_set_default_prefix()
demoRedBall/CMakeLists.txt:    icubcontrib_add_uninstall_target()
demoRedBall/CMakeLists.txt:yarp_install(FILES ${conf}    DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECT_NAME})
demoRedBall/CMakeLists.txt:yarp_install(FILES ${scripts} DESTINATION ${ICUBCONTRIB_APPLICATIONS_TEMPLATES_INSTALL_DIR})
demoYoga/CMakeLists.txt:list(APPEND CMAKE_MODULE_PATH ${ICUBCONTRIB_MODULE_PATH})
demoYoga/CMakeLists.txt:icubcontrib_set_default_prefix()
demoYoga/CMakeLists.txt:    icubcontrib_add_uninstall_target()
demoYoga/CMakeLists.txt:yarp_install(FILES ${conf}      DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECTNAME})
demoYoga/CMakeLists.txt:yarp_install(FILES ${yoga}      DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECTNAME}/yoga)
demoYoga/CMakeLists.txt:yarp_install(FILES ${crf}       DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECTNAME}/crf)
demoYoga/CMakeLists.txt:yarp_install(FILES ${hannover}  DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECTNAME}/hannover)
demoYoga/CMakeLists.txt:yarp_install(FILES ${two-hands} DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECTNAME}/two-hands)
pf3dBottomup/CMakeLists.txt:list(APPEND CMAKE_MODULE_PATH ${ICUBCONTRIB_MODULE_PATH})
pf3dBottomup/CMakeLists.txt:icubcontrib_set_default_prefix()
pf3dBottomup/CMakeLists.txt:    icubcontrib_add_uninstall_target()
pf3dBottomup/CMakeLists.txt:yarp_install(FILES ${conf}    DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECT_NAME})
pf3dBottomup/CMakeLists.txt:yarp_install(FILES ${models}  DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECT_NAME}/models)
pf3dTracker/CMakeLists.txt:list(APPEND CMAKE_MODULE_PATH ${ICUBCONTRIB_MODULE_PATH})
pf3dTracker/CMakeLists.txt:icubcontrib_set_default_prefix()
pf3dTracker/CMakeLists.txt:  icubcontrib_add_uninstall_target()
pf3dTracker/CMakeLists.txt:yarp_install(FILES ${conf}    DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECT_NAME})
pf3dTracker/CMakeLists.txt:yarp_install(FILES ${models}  DESTINATION ${ICUBCONTRIB_CONTEXTS_INSTALL_DIR}/${PROJECT_NAME}/models)
pf3dTracker/CMakeLists.txt:yarp_install(FILES ${scripts} DESTINATION ${ICUBCONTRIB_APPLICATIONS_TEMPLATES_INSTALL_DIR})