News listing view: handle news without effective date.

The effective date may not be set (year~=1000), which causes the news listing to fail with:
ValueError: year=999 is before 1900; the datetime strftime() methods require year >= 1900
News archive portlet: handle news without effective date.

The effective date may not be set (year~=1000), which causes the news listing to fail with:
ValueError: year=999 is before 1900; the datetime strftime() methods require year >= 1900
Merge pull request #59 from 4teamwork/jone-news-without-effective-date

News: handle news items without effective date