Start port to QSharedPointer:
- the current live time handling is no standard C++ idiom
- implementing a shared pointer is legacy code from KDE 3
- QSharedPointer is a bullet proofed Qt class
- better encapsulation: objects should not know how they are stored (remove inheritance from Shared)
- define KST_USE_QSHAREDPOINTER in sharedptr.h to enable new code

One problem is the pointer -> SharedPointer transition, because mostly there exists already
a QSharedPointer for the object Qt asserts. Could be solved with a consequent usage of shared pointers.
Don't know why raw pointers are used.