UI on composing breaks when post is longer than screen space

[krl]

This is mostly against #25 , which contains some changes to how the editor is styled. (it did however not work before either)

@RichardLitt Could you have a look if you could get the main textbox to flex to the whole height, and also have its own scrollbar?

[RichardLitt]

This is my first time working with basic-web-components, but it looks like this is actually supposed to happen, since you're using basic-autosize-textarea. To fix this, we'd need to not use this component.

Why are we using it, and not just a large enough textarea box to fill screen?