Annotation tab does not display anymore

This regression probably happened before version 15.10.X .
Even with the `display annotation` administration option turned on, the annotation Tab in the document extra tabs does not appear anymore.
This is somewhat okay since this is not the default setting, and annotations can still be viewed in the comments Tab, however it's a shame to have all the code to support an independant Tab and effectively never use it.

From a quick look, this might be because the preferences got reorganized and the code to check if the preference was good could not find anything anymore and defaulted to not displaying a tab, whatever the preference...

Tested on Firefox and Chrome,
XWiki default flavor 16.1.0-snapshot
and some old XWiki default flavor 15.10.5-snapshot
Jetty + hsqldb