[Development] Use of Standard Library containers in Qt source code

[Philippe]

> The only thing worse than code you don't understand is code that you 
> misunderstand.

Very wise remark !

> STL was standardized 18 years ago, I think it should be enough to get used to empty().

A bad name remains a bad name. The mind has more important energy to
spend than "getting used to".

Option 3 has my vote.

Philippe