Improving notebook diff experience

[nikhilk]

Various things put out object memory locations which always change from run to run. Some offenders:

• matplotlib
• bq udf functionevaluation, querystats

Some things naturally will be different

• execution counters
• data (and derivatives -- images, html etc.)
• html ids

We should offer an option to the user to easily strip out outputs if thats interesting to them in their workflow for the latter category.

[nikhilk]

One other thing that would help -- nicely formatted HTML, so its not all one single line. Breaking it out would help identifying what changed.

[gramster]

Potentially we could strip out memory addresses by registering a formatter for object.

[nikhilk]

Well some of those things make no sense to even render, so its not just a serialization thing.