Adding missing __init__ files for packages (#97)

Summary:
__init__.py files are required to earmark folders as python packages. The wheel building process doesn't pick up these folders without it.

Manually tested wheel creation and these files were not getting packaged. They do now.

<!--- What types of changes does your code introduce? Put an `x` in all the boxes that apply: -->
- [ ] Docs change / refactoring / dependency upgrade
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
<!--- If you're unsure about any of these, don't hesitate to ask. We're here to help! -->
- [x] My code follows the code style of this project.
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [x] I have read the **CONTRIBUTING** document.
- [x] I have completed my CLA (see **CONTRIBUTING**)
- [ ] I have added tests to cover my changes.
- [x] All new and existing tests passed.
Pull Request resolved: #97

Reviewed By: seayoung1112

Differential Revision: D13457047

Pulled By: snisarg

fbshipit-source-id: 9c4fa2e8a8c1dbb5e5ca63540d1581aa8d6ab78c

pytext/common/__init__.py

@@ -0,0 +1,12 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
+
+from .constants import (
+    BatchContext,
+    DatasetFieldName,
+    DFColumn,
+    PackageFileName,
+    Padding,
+    Stage,
+    VocabMeta,
+)

pytext/data/data_structures/__init__.py

@@ -0,0 +1,2 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

pytext/models/language_models/__init__.py

@@ -0,0 +1,2 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

pytext/models/representations/__init__.py

@@ -0,0 +1,2 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

pytext/models/semantic_parsers/__init__.py

@@ -0,0 +1,2 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

pytext/models/semantic_parsers/rnng/__init__.py

@@ -0,0 +1,2 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

pytext/models/seq_models/__init__.py

@@ -0,0 +1,2 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

pytext/utils/__init__.py

@@ -0,0 +1,2 @@
+#!/usr/bin/env python3
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved