Tightly pack the texture with multilevel sort
- 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
Refactor box layout optimization into separate layouter
- Extend AbstractLayouter so subclasses can provide an
  implementation for OptimizeLayout
Made rounding of size to a multiple user adjustable and stored in config
Merge branch 'optimize_layout' of https://github.com/doug65536/fontbuilder into doug65536-optimize_layout

Conflicts:
	FontBuilder.pro