Draft: Rotation compensation

[simonschmidt]

See #27

• Compensate when displaying highlights (scaledToViewport)
• Compensate when creating highlights (viewportToScaled)
• Can create highlights correctly...

[simonschmidt]

I added something similar in viewportToScaled but that was not sufficient to make adding highlights work...

I think because in MouseSelection the viewportPosition is not actually in viewport coordinates when we're dealing with rotated pages.

But I'm not sure, I'll leave this issue for the moment as I'm not even sure this is the right approach, maybe there's a way to ignore all the rotation stuff in the first place?

Particularly since currently the highlights component is placed inside the PDF.js textLayer which in turn has the rotation applied to it on CSS level - quite an impedance mismatch.

Would it make more sense to add a separate layer instead that PDF.js doesn't even try to rotate in the first place? (i.e. a div with the same size) Then highlights could just be added in there without knowing or caring about pdf rotation (EDIT: See #30 for this)