CMake: proposal to downgrade missing 3rdparty optional dependencies from warning to regular messages

[SergioRAgostinho]

It's necessary to report that we don't find them but I believe that all this clutter (see below) is not really necessary. A single line should suffice.

I admit it's a matter of taste but if others are on board with this it would be cool to change it.

-- Could NOT find OpenNI (missing: OPENNI_LIBRARIES OPENNI_INCLUDE_DIRS) 
CMake Warning at cmake/pcl_targets.cmake:864 (message):
  OpenNI grabber support: not building because OpenNI not found
Call Stack (most recent call first):
  CMakeLists.txt:315 (PCL_ADD_GRABBER_DEPENDENCY)


-- Could NOT find OpenNI2 (missing: OPENNI2_LIBRARIES OPENNI2_INCLUDE_DIRS) 
CMake Warning at cmake/pcl_targets.cmake:864 (message):
  OpenNI2 grabber support: not building because OpenNI2 not found
Call Stack (most recent call first):
  CMakeLists.txt:316 (PCL_ADD_GRABBER_DEPENDENCY)


-- Could NOT find FZAPI (missing: FZAPI_LIBS FZAPI_INCLUDE_DIRS) 
CMake Warning at cmake/pcl_targets.cmake:864 (message):
  Fotonic camera support: not building because FZAPI not found
Call Stack (most recent call first):
  CMakeLists.txt:317 (PCL_ADD_GRABBER_DEPENDENCY)


-- Could NOT find ENSENSO (missing: ENSENSO_LIBRARIES ENSENSO_INCLUDE_DIRS) 
CMake Warning at cmake/pcl_targets.cmake:864 (message):
  IDS-Imaging Ensenso camera support: not building because Ensenso not found
Call Stack (most recent call first):
  CMakeLists.txt:318 (PCL_ADD_GRABBER_DEPENDENCY)


-- Could NOT find davidSDK (missing: DAVIDSDK_LIBRARY DAVIDSDK_INCLUDE_DIR) 
CMake Warning at cmake/pcl_targets.cmake:864 (message):
  David Vision Systems SDK support: not building because davidSDK not found
Call Stack (most recent call first):
  CMakeLists.txt:319 (PCL_ADD_GRABBER_DEPENDENCY)


-- Could NOT find DSSDK (missing: DSSDK_LIBRARIES DSSDK_INCLUDE_DIRS) 
CMake Warning at cmake/pcl_targets.cmake:864 (message):
  DepthSense SDK support: not building because DSSDK not found
Call Stack (most recent call first):
  CMakeLists.txt:320 (PCL_ADD_GRABBER_DEPENDENCY)


-- Could NOT find RSSDK (missing: RSSDK_LIBRARIES RSSDK_INCLUDE_DIRS) 
CMake Warning at cmake/pcl_targets.cmake:864 (message):
  RealSense SDK support: not building because RSSDK not found
Call Stack (most recent call first):
  CMakeLists.txt:321 (PCL_ADD_GRABBER_DEPENDENCY)

[taketwo]

👍 this does not need to be a warning, a status message would do.