New coding policy standards which should be use in Calligra master

Use Q_SLOTS ans Q_SIGNALS instead of slots/signals keywords we used before
Add Q_DECL_HIDDEN to all nested Private classes in new code. A::Private need their symbols hidden, APrivate class does not, as it does not inherit the visibility from A.
instead of #include <QDebug> and #include <kdebug.h> use #include <kis_debug.h>
Use QUrl instead of KUrl and keep in mind that QString s; QUrl u = s; becomes QUrl u = QUrl::fromUserInput(s) or QUrl::fromLocalFile(s);