remove partially filled validation error on clear

[jelhan]

Change event is not triggered on clear if field was only partially filled. Therefor validation error may not be cleared if only relying on change event. It should at least also be removed if element loose focus.

It would be even better if validation error is updated directly after user clears the input. But that's not an easy one as neither change nor input element are triggered reliable. But as far as I've tested it should work by listening to this events:

• keyup evnet is fired if input is cleared with keyboard (e.g. backspace).
• focusin event is fired if input is cleared using button provided by native UI. (input event is only fired if element does not have focus before.)

Please note that only Chrome is affected as that's the only browser showing that validation error.

Closes #281