Add : isExpended, diplaySelectedDateText

[nk54]

Hello, nice widget.
But it lacks a bit of customisable options.

It would be awesome to be able to specify the expended state with something like isExpanded.
Benefits :

• can be used both with isExpandable set to true or false.
• can set the initial state of the widget
  IMHO the isExpandable should just add the possibility to display the expendable icon and give to users the possibility to expand or note the calendar widget.

Another functionnality would be to allow us to use a boolean to decide whether we want to display the date in expendable mode.

A third possibility would be to be able to animate calendar when swiping. But less important, that's just for better UX.

Sadly, I just started Flutter so I'm not good enough (at the moment) to implement the features I mentioned and send a pull request. So I rely on someone's will to see those improvments.

Thanks for your attention. I wish everyone a good day !

[quentin7b]

Definitely need to be able to set the isExpanded to true by default at startup