Small fixes in CMake mechanism + rev 338

-Fix missing extra include dirs, libs dirs and libs in user
CMakeLists.txt
-Use only minimal list of gcc warning flags. To activate the extended
list, build NA62Analysis or UserDir manually by issuing "cmake -H.
-Bbuild -DFULL_WARNING=1" in their respective root directory (only once,
NA62AnalysisBulder.py can be used as usual afterwards)