ticket:10347: add U_FINAL and U_OVERRIDE for C++11 "final" and "override".

Added them to several "not for subclassing" classes.
Some exceptions:
* Commented out U_FINAL where there's an internal override needed.
* For tests, added "#define U_FINAL" at the top to disable this.
#defined to null for Doxygen.


git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@36177 251d0590-4201-4cf1-90de-194747b24ca1
ticket:11045: fix for glibc assumption


git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@36178 251d0590-4201-4cf1-90de-194747b24ca1