Reorganize repo (#8580)

* Put models in subfolders

* Styling

* Fix imports in tests

* More fixes in test imports

* Sneaky hidden imports

* Fix imports in doc files

* More sneaky imports

* Finish fixing tests

* Fix examples

* Fix path for copies

* More fixes for examples

* Fix dummy files

* More fixes for example

* More model import fixes

* Is this why you're unhappy GitHub?

* Fix imports in conver command

tests/test_modeling_tf_roberta.py

@@ -27,7 +27,7 @@ if is_tf_available():
     import numpy
     import tensorflow as tf
 
-    from transformers.modeling_tf_roberta import (
+    from transformers.models.roberta.modeling_tf_roberta import (
         TF_ROBERTA_PRETRAINED_MODEL_ARCHIVE_LIST,
         TFRobertaForMaskedLM,
         TFRobertaForMultipleChoice,