FIxes missing popups

[gtache]

Fixes #140

[pcorless]

This is interesting. So I'm guessing if you double-click on the parent annotation the popup component will be created and shown? But otherwise the popup is in an invisible on first load?

[gtache]

No, in fact it causes a NullPointerException in togglePopupAnnotationVisibility, as getPopupAnnotationComponent will return null because the PopupAnnotationComponent is not contained in the PageViewComponent components.
Here is the file causing this problem:
NoPopup.pdf