Add HTML component

[wwwillchen]

There's a couple open questions on the implementation, I'd like to get your thoughts on:

1. There's no styling inside the iframe. Should we inject the stylesheet in here?
2. The iframe height is arbitrary (browser default). Should we try to automatically resize the iframe based on the content or should Mesop app developers set a height?

Closes #156.

[richard-to]

1. There's no styling inside the iframe. Should we inject the stylesheet in here?

What do you mean by "inject the stylesheet"?

When using the iframe with source doc, is the user able to reference assets (Javascript, CSS) from other domains or would they need to reference from same domain? Or is that not allowed for security reasons?

I guess if linking to external resources is not allowed, then one could write the js/css in the html head. Probably not that user friendly, but since this is an advanced use case, probably ok. Although would be hard to manage.

2. The iframe height is arbitrary (browser default). Should we try to automatically resize the iframe based on the content or should Mesop app developers set a height?

I think the app developer should able to set the height. So if there is auto resize as a default and the user could resize as an override, that may be more convenient.

[richard-to]

LGTM

[richard-to]

[nit] Looks like these are pointing to "link" when it should be html?

[wwwillchen]

will re-open once I've been able to address the comments.