Add componentWillReceiveProps

[youreme]

Hi,

When DayPickerInput gets nextProps, it doesn't change its states.
How about adding componentWillReceiveProps lifecycles?

After it mounted,
if it doesn't trigger any change events, the value state is different from value property.

[coveralls]

Coverage decreased (-0.2%) to 99.817% when pulling 9d1d043 on youreme:develop into 099057d on gpbl:master.

[gpbl]

Thanks! I need to add a test before merging this :)

[gpbl]

Superseded by #365