Migration strategy with different versions of Storybook+VTA (so that there is only one filter UI)

[yannbf]

• Old VTA in new SB will use the new filter UI with no issue because the new filter UI uses the status API which the VTA has always used. Old filter UI is ignored (not applied).
• New VTA in old SB will still apply the old filter UI, and that will work as it used to. It will send an onClick property for the story statuses, but that will be ignored by the old SB.
• New VTA in new SB will try to apply the old filter UI but it will be ignored. Instead it will use the new filter UI.

[ghengeveld]

See chromaui/addon-visual-tests#332