use less bespoke serialization

[ianhi]

https://github.com/vidartf/ipydatawidgets looks great. handles thinks like compressing to avoid those nasty iopub errors

[ianhi]

seems to be broken up into multiple packages so its not crucial.

In particular checkout how the widget for images
https://github.com/vidartf/ipydatawidgets/blob/master/packages/jupyter-datawidgets/src/media.ts
https://github.com/vidartf/ipydatawidgets/blob/master/ipydatawidgets/ndarray/media.py

[ianhi]

its broken up into one python package and two different js packages:

• jupyter-datawidgets/jlabextension (provide the widgets - I don't need this)
• jupyter-dataserializers