Allow extension widgets to set widget-content-classes

[DallasHoff]

Feature request: provide a mechanism for extensions to add additional CSS classes to widget-content, similar to how the built-in widgets' templates can define widget-content-classes.

My use case is a custom video carousel. It is based on the built-in videos template, but that template adds a widget-content-frameless class to remove the default widget frame. To replicate that, I would have to inject a script with the extension response, so I think it would be good to provide a better method to accomplish this.

The obvious way I see of doing this would be to allow extensions to return a Widget-Content-Classes response header. What do you think?

[svilenmarkov]

Hey, thanks for bringing this up, it's something that's been on my todo list for a little bit now. I would however do it slightly differently where instead of allowing the extension to define classes, I'd add a Widget-Content-Frameless: true option. This just makes it a little more future-proof so that if the internal mechanism of how this works changes, the functionality still works without needing to change anything on the extension side.

[DallasHoff]

Yeah, that makes sense. Thanks!