Efficientnet

Fixes
- Fix `get_custom_objects()` (128)

Updates
- Add Noisy Student weights for b0-b7 models (`weights="noisy-student"`)

Stable release of EfficientNet
- keras and tf.keras support
- imagenet pretrained weights for b0-b7 models

1) Add B5 and B6 weights (thanks to Callidior)
2) Weights updated to better ones, trained with autoaugment (thanks to Callidior again)

Fix `swish` custom object deserialization

Improvements:

1) Support of `keras` and `tf.keras` frameworks
2) Preprocessing from `keras_applications`
3) Reduce number of custom objects
4) Tests

Changes
1) API changes (model import under framework modules)

Notes
1) Previously trained models are not compatible with current release, use `model.load_weights` function or roll back to previous version - v0.0.4