update_title option

[alexcjohnson]

A new feature to be released in the next Dash version (1.14.0) is update_title. This requires a minor addition on the back end to avoid a breaking change, because the renderer no longer holds the default "Updating..." page title. See https://github.com/plotly/dash/pull/1315/files#r455117288

[alexcjohnson]

#218 takes care of the breaking part of this issue (not sure why that didn't close this one even though it says it should 🤔 )
I'll note though that plotly/dash#1343 added a new constructor kwarg title. Here there's already a nice documented app.title(newTitle) method, whereas on the Python side it was an undocumented attribute app.title = newTitle. That said for parity and consistency with update_title it would be nice to be able to set the title via the app constructor here as well.