Add option custom ui date picker

[chuvanhoang888]

Hello Sir,
This is a great package, but can you add option customize the date range picker interface as below?

In my case, I need date range picker that returns the same start day and end day when double clicked on the same day

[hasanmhallak]

hey @chuvanhoang888, I add the ability to select the same date as a range, and to center the leading date as your image shows.

Unfortunately there is no possible way to customize the look of the page sliders without changing a lot of code which I don't have the time for. But I'm open to review any pull requests.