Added support for multiple component columns in XLFormPickerCell

XLFormPickerCell will display multiple component columns in the picker
view when the row descriptor’s selectorOptions is set to a
multidimensional array. The row descriptor’s value will be set to an
array of selected values from the components.
Added example for multi column picker.
Call valueData on row value when returning form values.
Merge branch 'picker-enhancements'