Added collapse to CellFilter

Signed-off-by: Alexander Kastius <alexander.kastius@student.hpi.uni-potsdam.de>
Merge branch 'racktables-html5' of https://github.com/acidix/racktables into racktables-html5
CellFilter reworked.

Signed-off-by: Alexander Kastius <alexander.kastius@student.hpi.uni-potsdam.de>