create class PenTool
* introduce PenTool into ScribbleArea
* rename currentTool() -> currentToolType()
move class Properties to basetool.h
reorder properties' code
remove unused code
add method loadSetting() into BaseTool
add member QHash<ToolType, BaseTool> m_toolSetHash to store tools
reorder the settings loading
move field pen properties, from ScribbleArea -> PenTool
minor