Python supports multiple categories, no work really as python does not realy support categories any more.

refs #2128
Python and the mantidplot UI respects not showing algorithms if all of it's categories are hidden 

tests:
                  Normally  Hidden   What I want
in tree           Yes       No        No
in search box     Yes       No        No
typed in box      Yes       Yes       Ideally, but not too fussed
mtdHelp           Yes       No        No
intellisense      Yes       Yes       No, but not too fussed
typed in script   Yes       Yes       Yes