Added basic Cairo paint DC for wxQT (tentative)

This is a very minimal approach (drawing to a cairo image surface and not a qt surface), but will help to avoid crashing (for example, in drawing sample, even if qt surface is not available).
Implement missing font info constructor in wxQT

(This is also needed by the drawing sample)
Implement missing font family, weight & style getters
Fix font weight and underline setters
Fix font face name getter (using actual info from Qt)

It was returning an empty string (if no facename was given at the font ctor), and that caused a segmentation fault in cairo_show_text
Fix wxQtDCImpl::GetHandle() to return QPainter

This is needed by the grahpic context
Fix cairo image buffer paint DC in wxQT

* do not destroy the image as it holds the pixel data buffer
* hence, do not create a new image as it isn't necessary

This solution is similar to cairo qt surface internals, that stores image and image_equiv -the cairo image surface-.
Implemented wxBitmap::GetRawData in wxQT (similar to wxGTK)
Removed GetHandle (virtual) call from wxWindow dtor in wxQT
Postpone the shortcut handler destruction to avoid seg. faults
Fix missing __WXQT__ guard in include, thanks @seandepagnier
Fix uninitialized value causing 'Painter not active', thanks @seandepagnier
Add sanity checks for Qt event/signal handlers

 * Use the window pointer to detect if the class is dead or alive to avoid crashing caused by deleteLater() being processed in the event loop
 * Print debug messages if the handler (wxWindow) is NULL (deleted), just for safety and debugging as that code should not be reached if Qt signals are blocked or Qt events are filtered / removed (comming in future commits)
 * Set the window pointer immediatelly in wxQt helper template constructor to avoid problems if wxWindow base class was not fully initialized and a Qt event/signal is received

GetHandler will return NULL if the wxWindow object was deleted, so it should be verified in the signal handlers in each derived class (events are automatically verified by the helper)
Avoid crash if a control is deleted and a signal is received

For example, this could happen if the wxNotebook was deleted and there were pending singals (i.e., emmited due the removal of the current page).
This should not happen, signals will be blocked in the destructor in following commits, but this is in place just in case to avoid segmentation fauls (debug message will be print by the wxQT helper)
Block Qt signals if widget is being deleted

This avoid most of the problems caused by receiving a signal if the wxWindow is deleted (for example, notebook changing the default page, see previous commits).
I've tried two other methods without success:
 * m_qtWindow::disconnect() should do the disconnection of all signals but returns false
 * QApplication::instance()->removePostedEvents(m_qtWindow); seems to have no effect (also, installEventFilter could be used)
Derive list control from wxListCtrlBase in wxQT

This fixes missing methods compilation errors: EnableBellOnNoMatch, EnableAlternateRowColours, AppendColumn and OnGetItemAttr
Use the correct widget QTreeWidget and helper for list control
Implement column insertion basics in wxQT list ctrl
Implement basic item insertion in list ctrl
Implement set item in list ctrl

(and item count and insert item return value)