* Improve neural-networks (and include bonus note)

* Improve interactive component
* Fullscreen button
* Load from a different lesson
* More flexible `children` function

* Create lesson: gradient-descent

* Update testbed `Interactive` children usage

* Create lesson: neural-network-analysis

* Improve neural network interactive
* Fix scrolling bug
* Normalize input drawings for better results
* Create instant mode
* Add full screen feature to Interactive component

* Fix aspect ratio of neural nets interactive

* Display message while pre-processing

* Improve content of neural nets articles