Add 3D operations for layers: conv3d, avg_pool3d, max_pool3d and conv3d_transpose (#9773)

* Add avg_pool3d operation for layers.

* Add max_pool3d operation for layers.

* Add conv3d and convolution3d operations for layers.

* The function loss_ops.get_regularization_losses() from tensorflow.contrib.losses.python.losses has been deprecated. Use tensorflow.python.ops.losses.losses.get_regularization_losses() to replace it.

* Add unit test for avg_pool3d.

* Add unit test for max_pool3d.

* Add conv3d_transpose and convolution3d_transpose for layers.

* Update layers.py

Add a missing line break

* Update layers_test.py

Change from importing methods to import at module level.

* Update RELEASE.md

Add the description for `conv3d`, `avg_pool3d`, `max_pool3d` and `conv3d_transpose`.

* Update RELEASE.md

Update to Version 1.2

* Revert "Update RELEASE.md"

This reverts commit a8ae1fedd3d3695bd0266732083d89b3af9f8ca1.

* Revert "Update RELEASE.md"

This reverts commit 7b8c5eb6bdbd28387adf3afbfc8b49375ed0e2c8.

* Add a missing declaration

Add missing conv3d declaration or slim.conv3d cannot be found.

* Update layers_test.py

Put the imports in alphabetical order

* Update BUILD

Add dependency.

* Update BUILD

* Update BUILD

* Update BUILD