Uniformizes initial popup size

[gtache]

Closes #328
Also allows setting default height and width with properties.

[pcorless]

This approach works OK at the 100% zoom but the popup size will vary as the zoom changes. I would probably recommend a fix where in the inverse of page transform is used.

try { pageInverseTransform = pageInverseTransform.createInverse(); } catch (NoninvertibleTransformException e) { throw new RuntimeException(e); }
The current implementation has a bug in the current page transform is used. With the above change the popup box will always be the same size no matter the zoom level relative to the page size. Please let me know if I misunderstood the intent.

[pcorless]

Here's an example of the inverse transform in use. The annotations where created at three different zoom levels and you can see the popups are all the same size.

[gtache]

Thanks for the fix! I'll check if this is exactly what we want but I'm pretty sure it is, so I'm closing this PR for now.