NcDatetimePickers do not match the consistent NcAction style

[susnux]

With #3784 (thanks to @raimund-schluessler ) almost all NcAction... have a consistent style , except the DatePicker.

• The default NcDatetimePicker
  • does not use a material icon so the icon stands out from the other actions.
  • does not have the same border style
  • the right margin of the icon looks smaller than the others (but might be only because of the different icon style)
• The native NcDatetimePicker
  • looks like there is too much margin on the right side of the icon (compared to the other icons, like for password input or the submit on text inputs) (not possible, see comments below)

[raimund-schluessler]

The icon for the native datepicker comes from the browser, and I couldn't figure out a way how to style it yet (or even just remove it to put a custom one).

[susnux]

The icon for the native datepicker comes from the browser, and I couldn't figure out a way how to style it yet (or even just remove it to put a custom one).

Indeed, seems like only webkit browsers allow styling the icon.