Krita/docs/NewCodingPoliciesInMaster

New coding policy standards which should be use in Calligra master

1. Use Q_SLOTS ans Q_SIGNALS instead of slots/signals keywords we used before
2. Add Q_DECL_HIDDEN to all Private classes in new code
3. instead of #include <QDebug> and #include <kdebug.h> use #include <kis_debug.h>