Add 2BPP tests
Add 2BPP helper functions for our blocks.

Namely, there are two things that we need to do:
1. Figure out the sub-mode based on the mode bit and the structure of the modulation data. The comments in Block.h describe how we do this.
2. For a given texel index, return 2BPP texel modulation bits.
Fix bug with debug images
Add unpack RGBA for our pixels
Decouple upscale directions so that we can non-uniformly scale images.
If our compile flag is set to output debug images with tests, then actually do it.
Add 2BPP decompression
Refactor debug output for modulation info.
Remove dead code