Add weight initialization as a parameter to layers

[sgrosser]

tf.initializers offers several initializers we can use. Maybe give a dropdown rather than an text field for this one. We could offer zeros, ones, uniform random, and Xavier (implementable with tf.initializers.varianceScaling(scale=2).

This would be used for the Obedience Training story.

[martinjm97]

This would be a dropdown in the parameters section?

[sgrosser]

As in a < select > instead of an < input >

[sgrosser]

@martinjm97 would we want an "advanced" parameters checkbox somewhere which would reveal stuff like this? Or should we stick with no toggles in our UI? I just don't want there to be too many parameters.