2-way data serialization

Today, Dash serializes all components to JSON before sending them to the browser. This means that any component properties passed in must be valid JSON, so Python objects are not valid inputs.

This means it's a bit tricky to create a grid. Using a dataframe, you might expect: grid = dash_ag_grid.AgGrid(dataframe=df) to just work. However, you must convert your dataframe to JSON first. The same is true on the way back in for callbacks. With 2-way serialization, Dash components could accept Python objects with no type conversion required by the developer.