DateTimeEditWCalendarTime: fix inconsistncies

In https://github.com/biolab/orange-widget-base/pull/153 is noticed:

> After some further investigation I noticed: if one changes only the month or the year it does not reflect on the value, wheres changing the date or the time does. Besides, when changing the date, the popup closes, meanwhile changing anything the popup remains open. I can merge the PR, because it fixes a bug, but I disagree with the inconsistency.

I am opening this PR that we do not forget about this.

Start by reviewing pull request 153 and locating the DateTimeEditWCalendarTime implementation in orange-widget-base. Reproduce the month/year versus date/time update behavior and the popup closing behavior; done means the component no longer treats these changes inconsistently.

Written by the indexing model from the issue text.