brewrenderer cleanup

[5e-Cleric]

I found this accidentally while fixing a toolbar issue.

We define the page height arbitrarily in brewRenderer to use to calculate scrolls and stuff. I know the function still works, but i assume this code could be cleaner.

In addition, this code calculates the height to establish in the brewRenderer element:

However, A height of 100vh, works just fine, given other adjustments that make sense to have the toolbar there.

I preferred to make an issue for this rather than cluttering the gitter chat.

[5e-Cleric]

To clarify, these features were made 8 years ago, viewport units did not exist.

[5e-Cleric]

will be fixed by #3694