Setting `DP_MODELS_PATH` and `DP_DOWNLOADS_PATH` variables doesn't really work

Created by: my-master

All configs in DeepPavlov library have their own way of what is written in MODELS_PATH:

• some configs have just {ROOT_PATH}/models
• some configs have one more folder, ex. {ROOT_PATH}/models/kbqa_mix_lowercase
• some configs have a lot of additional folders, ex. {ROOT_PATH}/models/classifiers/insults_kaggle_v3

This makes pointless setting DP_MODELS_PATH environment variable because it will overwrite MODELS_PATH and all paths that have additional folders cannot be found then.

I think it could be fixed by standardizing MODELS_PATH in all configs as {ROOT_PATH}/models, and all additional folders should be in a different variable ( MY_FOLDER = {MODELS_PATH/whatever/folders}).