add a `validate=False` option for `graph_objects` and `px` figures

There's already an issue outlining the effects graph_object validation has on plot generation time. Users can bypass this performance hit by replacing the graph_objects with dict and then display the plot with plotly.offline.iplot(fig, validate=False) or if they are creating graphs in Dash, they can forgo the plotly.py library altogether and just use a dict in their Graph component's figure argument.

This solution can greatly improve the performance of Dash apps but it means that Dash users with expensive graphs have to choose between using px/plotly.py's update methods and optimally fast code.

I wonder if a way to turn off validation, especially in Dash apps, would help Dash users get the best of both worlds.

cc @matthewchan15

Review issue #1052 and the existing graph_objects and px figure-generation paths, then trace how validation is applied before offline.iplot and related figure consumers. Define how a validate=False option should work across these APIs, including the Dash use case, and verify that disabling validation improves the targeted path without changing normal validated behavior.