Vendor pretrainedmodels

[adamjstewart]

Same as #1036

Pretrainedmodels doesn't have wheels on PyPI, and is no longer maintained. It contains numerous Python version compatibility issues as well. Let's vendor it and maintain it ourselves. This will make SMP easier to install.

We can and should try to deprecate these in favor of timm in the long run. This PR doesn't do that though.

[codecov]

Codecov Report

Attention: Patch coverage is 65.25516% with 320 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
segmentation_models_pytorch/encoders/_dpn.py	52.77%	119 Missing ⚠️
segmentation_models_pytorch/encoders/_senet.py	55.29%	76 Missing ⚠️
...tion_models_pytorch/encoders/_inceptionresnetv2.py	74.86%	47 Missing ⚠️
segmentation_models_pytorch/encoders/_xception.py	64.34%	46 Missing ⚠️
...gmentation_models_pytorch/encoders/_inceptionv4.py	81.60%	32 Missing ⚠️

Files with missing lines	Coverage Δ
segmentation_models_pytorch/__init__.py	92.85% <ø> (-0.70%)	⬇️
segmentation_models_pytorch/encoders/dpn.py	93.87% <100.00%> (ø)
...ation_models_pytorch/encoders/inceptionresnetv2.py	94.82% <100.00%> (ø)
...egmentation_models_pytorch/encoders/inceptionv4.py	92.68% <100.00%> (ø)
segmentation_models_pytorch/encoders/senet.py	93.02% <100.00%> (-0.16%)	⬇️
segmentation_models_pytorch/encoders/xception.py	94.82% <100.00%> (ø)
...gmentation_models_pytorch/encoders/_inceptionv4.py	81.60% <81.60%> (ø)
segmentation_models_pytorch/encoders/_xception.py	64.34% <64.34%> (ø)
...tion_models_pytorch/encoders/_inceptionresnetv2.py	74.86% <74.86%> (ø)
segmentation_models_pytorch/encoders/_senet.py	55.29% <55.29%> (ø)
... and 1 more