Port basic layer functionality in order to add TF.Keras support

[chriss2401]

In order to support basic TF.Keras layers (i.e. the Dense layer), basic classes need to be binded - ported such as :

• Trackable - https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/training/tracking/base.py#L529
• AutoTrackable - https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/training/tracking/tracking.py#L52
• Module - https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/module/module.py#L35
• Layer - https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/keras/engine/base_layer.py#L104

Then something like Dense can be ported:
https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/keras/layers/core.py#L1067

[Oceania2018]

@chriss2401 It's partially supported since preview3.