Port QAbstractItemView and dervied classes to pmf-style connects

All ItemView classes (derived from QAbstractItemView) should be ported to pmf-style connections. Since thoses classes depend on each other they can't be ported one by one but need to be ported together.
To split this task into oversseable sub-tasks the following parts should be done sequentially:

• port to pmf-syntax incl. disconnect the connections in the dtor to avoid assertions whe a signal/slot is triggered in the dtor and the receiver is already destructed
• remove Q_PRIVATE_SLOT() macros
• rename all _q_Foo() private slots to foo() (safe now since this will create a compiler error when it's used in another itemview class somewhere)