Fix and update codebase & pre-trained models with demo samples

1. Fix variance adaptor to make it work with all combinations of building block and variance type/level
2. Update pre-trained models with demo samples of LJSpeech and VCTK under "transformer_fs2" building block and "cwt" pitch conditioning
3. Share the result of ablation studies of comparing "transformer" vs. "transformer_fs2" paired among three types of pitch conditioning ("frame", "ph", and "cwt")