Consider making WidgetBase abstract and not implementing render

[agubler]

Enhancement

We should consider making WidgetBase abstract and not implementing the render method. There isn't really a use-case to for WidgetBase to not be extended and making it abstract would ensure that the render method is correctly implemented by sub classes.

[kitsonk]

There was a time where I disliked the concept of abstract in TypeScript, given interfaces, but I have realised over time, something like WidgetBase is perfect for that sort of concept. No one should ever use it directly, therefore, it is, in its own right, an abstract class.

[kitsonk]

I think this is 👍, scheduling for beta5.