Extraction and adaptation to python 3.7+ of Facebook FairSeq DynamicConv

Fairseq has a dependency to sacrebleu which depends on other packages such as typing which produce a problem with python >=3.7.

Also the module for Dynamic Convolution does not have the correct imports having a few issues:

import fairseq.modules.dynamicconv_layer
---------------------------------------------------------------------------
ModuleNotFoundError                       Traceback (most recent call last)
<ipython-input-7-a398363c1102> in <module>
----> 1 import fairseq.modules.dynamicconv_layer

ModuleNotFoundError: No module named 'fairseq.modules.dynamicconv_layer'

This package tries to fix this and make the Dynamic Convolution package independent from the rest of fairseq.

The license is just the same as the fairseq license