DatePicker: disable input on mobile
Closes #4577
This PR disables the input it DisableMobile is enabled. I have also set DisableMobile with default false, par flatpickr documentation.
The only problem is that the input is shown as grayed like it has a disabled state. I don't know if that is the right behavior for the flatpickr.
Example

@Mr-Pearce do you think this is OK?
It will probably confuse users when the form is greyed out as if it is disabled but is enabled just that the keyboard wont show up.
I have to agree with Mr.Pearce, If I'm a user I would think its disabled by some reason. Isn't there a better way to represent that text is disabled but you can interact with it?
@stsrki friendly reminder, this PR sitting here
@stsrki friendly reminder, this PR sitting here
I know. I still didn't have much time to fix an error on flatpickr side. Which we must do before even applying it here.
Just a friendly reminder, @stsrki