[TTS] Try to train a universial GAN Vocoder using CSMSC + LJSpeech + AISHELL3 + VCTK

An universial GAN Vocoder may works well for all AMs of different datasets, for example, CSMSC is a single female dataset, may generate bad wavs for mels of male speakers, cause different genders have different distribution of speech features.

Please try to train a universial GAN Vocoder using CSMSC + LJSpeech + AISHELL3 + VCTK + some other TTS datasets (if you want) with the config of CSMSC (24kHz).

LJSpeech is 22.05kHz, but you don't need to resample it yourself, cause we will resample the wavs to the sample rate setted in config file in preprocess stage ~