Only one category can be selected.
Binding refactored.
Style moved to Expander.
Merge branch 'Sitrus2' into DUI-OnlyOneOpenCategoryAtTime
delete empty row
IsExpanded directly in Expander, style removed.
Merge pull request #2287 from vmoyseenko/DUI-OnlyOneOpenCategoryAtTime

MAGN-4378: Only 1 library category is open at a given time