code: function extendCell (cell, cellDefinitions) {
    cell = _.clone(cell)
    while (cell.extends) {
      const extendedCell = cellDefinitions[cell.extends]
      if (!_.isObject(extendedCell)) {
        throw new Error(`'${cell.extends}' is not a valid model definition`)
      }
      delete cell.extends
      cell = _.defaults(cell, extendedCell)
    }
    return cell
  }
docs: Copies a cell. If the cell extends cell definions, properties from teh extended cell
  are copied into the new cell.
  
  @param {BunsenCell} cell Cell to build up with cell definitions
  @param {Object} cellDefinitions Cell definitions available in the view
  @returns {BunsenCell} The expanded cell