Fix AuthMethodPickerActivity title being "ui_flow" instead of app name

[SUPERCILEX]

We want it to be overridden.

[samtstern]

Thanks! Good catch.

[WillieCubed]

Hey, we should probably document this since we're requiring an app_name string to override the library's. Is the best idea for usability, though?

[samtstern]

@SUPERCILEX there was no behavior change in recent versions regarding app_name right?

[SUPERCILEX]

@samtstern Nope, we've always used app_name because it's the default thing for AppCompat. We should probably put it on our mental list of stuff to fail the build in v3.0 if the dev doesn't supply it.