add a key to rendered column checkboxes in GridSettings
add a key to rendered column checkboxes in GridSettings

fixes issue #107

GriddleGriddle/Griddle,johanneshilden/Griddle,GriddleGriddle/Griddle,aphillipo/Griddle,bnchdrff/griddle-react,rovolution/Griddle,Jravvit/Griddle,aphillipo/Griddle,joellanciaux/Griddle,oToUC/Griddle,Shop2market/Griddle,Kikonejacob/Griddle,bnchdrff/griddle-react,johanneshilden/Griddle,ntdat3011/Griddle,saary/Griddle,Ent-ch/Griddle,Sipree/Griddle,namjul/Griddle,joellanciaux/Griddle,kevinold/Griddle,amorphousxd/griddle-ets,ttrentham/Griddle