simplify addItem/removeItem in basis.data.AbstractDataset#compute
simplify addItem/removeItem in basis.data.AbstractDataset#compute

tyanas/basisjs,smelukov/basisjs,basisjs/basisjs,istrel/basisjs,tyanas/basisjs,istrel/basisjs,basisjs/basisjs,basisjs/basisjs,tyanas/basisjs,fateevv/basisjs,smelukov/basisjs,fateevv/basisjs,fateevv/basisjs,istrel/basisjs,smelukov/basisjs