Allows use of an array of date formats

Moment.js allows use of an array of date formats when parsing dates.

This means that you can do... `moment('05/05/1945', ['dd/mm/yyyy', 'dd-mm-yyy'])` and `moment('05-05-1945', ['dd/mm/yyyy', 'dd-mm-yyy'])` and both will work. Moment will keep trying the formats in the array until it finds the correct one to parse it with.

I have updated the date picker to accept an array for the 'format' parameter. It then uses the first format in the array as the display format.
Hi @eddielee6, thanks by your PR, it is a nice feature!

My only concern is about the third boolean parameter (_strict parsing_). From [Moment.js documentation](http://momentjs.com/docs/#/parsing/):

> Moment's parser is very forgiving, and this can lead to undesired behavior. As of version 2.3.0, you may specify 
> a boolean for the last argument to make Moment use strict parsing. Strict parsing requires that the format and 
> input match exactly.
>
> ```
> moment('It is 2012-05-25', 'YYYY-MM-DD').isValid();        // true
> moment('It is 2012-05-25', 'YYYY-MM-DD', true).isValid();  // false
> moment('2012-05-25', 'YYYY-MM-DD', true).isValid();        // true
> ```

It means that our old parsing behavior is going to change. 

Another alternative is to use _strict parsing_ only for array of date formats and not for string format.

What do you think?