Tightly pack the texture with multilevel sort

[doug65536]

• Also round width and height to a multiple of 4 pixels to ensure 32-bit alignment when using 8-bit/pixel formats and to optimize OpenGL texture compression

[andryblack]

this features must be optional. e.g. subclass BoxLayouter as SortedBoxLayouter. 32pixel align must be optional too, for this need more complex code refactoring. All layouters may contain list of texture-size-generators. Sorry for bad english.

[doug65536]

I have updated my pull request. I refactored the optimizer into a separate layouter, which is based on the existing box layouter.

I extended AbstractLayouter to have a virtual OptimizeLayout(QVector<LayoutChar>&) which gives an opportunity for the layouter to optimize the layout. If the subclass doesn't implement OptimizeLayout, an empty implementation is provided by AbstractLayouter.

I made a new class BoxLayouterOptimized which inherits BoxLayouter, that implements OptimizeLayout.

I updated the optimizer sort to use qSort instead of C++ std::sort. The comparator is now a function instead of a functor.

I added a new spinner to the GUI, which lets the user adjust the rounding of the size to a given multiple. I have extended the layout config appropriately.

[andryblack]

Thanks