add notice that project will be built in Release mode

catkin_lint (rightfully) complains about this block that might
change CMAKE_BUILD_TYPE. Even so, without this block most people using
the git checkout (building locally) would wonder why MoveIt! is so slow
as they didn't specify Release build. So this will stay in here.
Nevertheless I suppose it's a good idea to leave a notice on the changed
build type in the logs.

CMakeLists.txt

@@ -2,6 +2,7 @@ cmake_minimum_required(VERSION 2.8.3)
 project(moveit_core)
 
 if(NOT CMAKE_CONFIGURATION_TYPES AND NOT CMAKE_BUILD_TYPE)
+  message("${PROJECT_NAME}: You did not request a specific build type: Choosing 'Release' for maximum performance")
   set(CMAKE_BUILD_TYPE Release)
 endif()