[DevExp] More graceful deprecation of old button

[alfonso-paella]

We're changing the API significantly with #28 , and may break devs who upgrade and suddenly nothing compiles

I was thinking we can do:
1/ Write a migration guide
2/ Keep the old and components, so that stuff compiles, but then all they do is throw an Error or even display an alert that says "You've upgraded to a new version of the SDK with breaking changes. Visit <link to migration guide> to learn how to fix this in under 5 minutes"