Also single date

It displays a single calendar so the user can pick just one date
In order to work it needs a config option: `this.withSingleDate: true`
That option enables a new item just above the 'Custom Range' named 'Specific Date'
This new item can be named anyway through the `locale: {}` config options object.
In order to minimize the refactoring, is the best solution that I can come with, right now.
I am just happy to know is on the right path, and make me the comments you see are in need; if you want to incorporate this in your project.
Thanks for this awesome DatePicker !!!