+ Added support to rotate images of IMAGE_BITMAP type.
+ Added transformation_handle & pivot_handle parts in sheet.png.
+ Added rotation cursors in sheet.png.
+ Added gfx::Transformation class and Document::m_transformation field.
+ Added StandbyState::Decorator and TransformHandles class to draw
transformation handles.
+ Modified PixelsMovement class to support transformation handles.
+ Added new Linear Algebra library with Vector2d class.