Changes:
- Remove the strange header-only variant of libs/image
- Rename KtxBundle => Ktx1Bundle
- Move image/KtxUtility => ktxreader/Ktx1Reader
- Add unit test for Ktx1Reader and test stub for KTX2.
Notes:
- Ktx1Bundle does not depend on Filament and is used by cmgen
and mipgen to generate KTX files.
- Ktx1Reader has a dependency on Filament and should therefore live in
a separate library, which it now does.
This tool was producing bad output for the monkey roughness map because
the monkey map has an (unnecessary) alpha channel, and the tool was
assuming that the source image has 3 channels.
This fixes that particular case and changes the tool so that it
operates on single-channel data instead of 3-channel data.
