Add Batch Mode to select a whole week or month

I did 3 things in this PR:
+ I make days in lastMonth and nextMonth also pickable
+ add batch mode feature to select a whole week or month
+ update moment.js to v2.6 for using the `startOf('isoweek')` method in batch mode feature

I'm not sure whether Batch Mode feature was generically needed.
Maybe we can have some discuss.