Added support for Signal/Slot lambda invokations

Also avoid a pedantic C90 warning and remove trailing whitespace.

Bumped to 5.15.2 and 5.12.11

This was due by multiple factors. The most important is that we always registered Models as DosQAbstractItemModelWrappers that is a subclass of QAbstractItemModel. This in turn broke the APIs when the user really instantiated a QAbstractTableModel from the binded language because the cast from DosQAsbstratItemModelWrapper to QAbstractTableModel failed.
The solution is to add different correct subclasses during registration