GF-5466: Add handler for monthPicker's changing event
GF-5466: Add handler for monthPicker's changing event

When monthPicker is updated, current value should be updated.

Enyo-DCO-1.1-Signed-off-by: David Um <david.um@lge.com>

mcanthony/moonstone,mcanthony/moonstone,mcanthony/moonstone,enyojs/moonstone