The function `assertWllFormed` was doing nothing different than `assert` which is
available in the same namespace. Removing it will lighten the filesize - albeit
very slightly - and reduce complexity.
Added an "InteractiveAnnotation" class to homogenize the annotations' structure (highlighting) and user interactions (for now, used for text and link annotations).
Text annotations:
The appearance (AP) has priority over the icon (Name).
The popup extends horizontally (up to a limit) as well as vertically.
Reduced the title's font size.
The annotation's color (C) is used to color the popup's background.
On top of the mouseover show/hide behavior, a click on the icon will lock the annotation open (for mobile purposes). It can be closed with another click on either the icon or the popup.
An annotation printing is conditioned by its "print" bit
Unsupported annotations are not displayed at all.
