AVX inverse DCT path for DWAA|B_COMPRESSION (and some minor reformatting to match coding conventions)

* Changing dctInverse8x8() from pre-processer decided impl to a runtime decided impl
   * The big change in dctInverse8x8_sse2() is an indent
   * All impl should at least be defined, but fallback to _scalar() if we not supported at compile time. This way we don't need to litter other code with pre-processor guards

* Added AVX iDCT, as inline 64-bit asm
   * Using intrinsics forces -march=asm, or similar, which will compile sse intrinsics to avx128, making backwards compatible builds difficult
   * Has the downside of not working with VS

* Minor reformatting in ```testDwaCompressor.cpp``` that escaped previous reformatting