Merge pull request #45 from seandepagnier/test

Fix crash caused when exiting (related to main window central widget focus signal)
Simplificate QWidget* assignment (new PostCreation method)

Also reducing the redundant m_qtWindow code, this could help to unify application of background style and default colors (for painting, that was not being enforced and could cause issues). Window style code is commented in the original, maybe it belongs to wxFrame.
PostCreation method name was taken from wxGTK, that has similar features.
Fix default widget fore/background colour
Implement missing wxQT helpers for QLabel

This now is needed to correctly paint the background, allows the static text / bitmap to handle events and signals, and maybe a better destruction process.
Fix default wxTextCtrl color background due PostCreation
Improve erasing issues (let Qt handle them)
Implement simple listctrl methods in wxQT
Refactory the list ctrl signal handler
improve top level window initialization
Implemented column getter and setter in listctrl
Fix row colours (fg/bg) in wxQT list ctrl
Fix font in listctrl row
Refactor get Qt list ctrl item to its own method
Implemented item text setter and getter
Refactor qt list item handling (check if not null)
Implement item data in wxQT list control
Implemented items and column deletion in wxQT list ctrl
Implemented item state getter and setter in wxQT list ctrl
Implement get next list item (adapted from generic) in wxQT
Implement item & subitem rect/pos in wxQT list ctrl