Pytorch-toolbelt

* Refactoring of activation functions factory method (for upcoming model builder)
* Cosmetic changes in logging

* Global pooling, SCSE module and MobileNetV3 encoders are not ONNX and CoreML friendly.
* Refactored FPN module for more flexible `interpolate_add` tuning (can use any module with two inputs)

Added MobileNetV3 encoder (implementation credits to https://github.com/Randl/MobileNetV3-pytorch)

New features

1. Added WiderResNet & WiderResNetA2 encoders (https://github.com/mapillary/inplace_abn)

Changes

- Added 10-Crop TTA (https://github.com/BloodAxe/pytorch-toolbelt/issues/4)
- Added unit tests for TTA functions
- Added `freeze_bn` function to freeze all BN layers in a model
- Rename `unpad_tensor` to `unpad_image_tensor` to mimick `pad_image_tensor`

Bugfixes

- Fixed bug in `d4_image2mask`

API Changes

1. Refactored TTA interface