Use boost::shared_ptr instead of plain pointer to handler KNArticle that are use all over the place.

Side effect: use a QList in KNArticleVector instead of a old fashion array

This fix crash cause by double free and freed-pointer access:
BUG: 172266
BUG: 225813
BUG: 141573
This should also fixed crash that happens while accessing article (that
were certainly already freed):
BUG: 134904
BUG: 216919
BUG: 230536
BUG: 132990

svn path=/trunk/KDE/kdepim/knode/; revision=1117909