[Qt-creator] C++11 in Creator's source: Update required features

[Guido Seifert]

Not sure about gcc, but with clang it is very easy to be consistent. Mark one function with 'override' and
you get a warning when you miss to put this keyword on all overridden functions in this class.

Guido


>      2) Make sure derived classes are consistent in their use of the 
> keyword, i.e. don't have overridden functions with and without the 
> keyword in the same class.