Allow all rotation angles

Fixes #194.

I hope my viewport calculations are correct.

I also have code which allows for pinch rotate, would you like me to create a PR for that too? If so, should I add an option for it?
It looks like this code is for making sure the navigator properly fits the content when the navigator container is resized. Have you tested resizing a viewer that contains a navigator when the image is tall or wide and rotated? That would be where this comes into play. 

I'm not sure why we don't just call `this.viewport.goHome()` in this situation, though.