_hidePrevMonthArrow should hide with css instead of style to not brake flexbox layout

[pastinepolenta]

Setting a minDate the prev month arrow hides. This is good but we should have more control on the way that the arrow is hidden. In my case, I am styling the entire calendar with flexbox and removing the arrow from the DOM causes a misalignment of the month name. It would be better to add a class like "flatpickr-hide" so that it can be easily overridden via CSS.

Here a fiddle: the month should stay center. I could achive that with prevMonth display block visibility hidden.
https://jsfiddle.net/stilllife/4fuwnLt6/

Any browser or OS