Prevent dates from breaking across lines

Start and end date of a date range may break across lines. This should
be prevented for certain languages (e.g., CJK languages).

Ideally, we should use "word-break: keep-all", which is not yet
supported by Chrome. Reference link:
https://code.google.com/p/chromium/issues/detail?id=141792
Until then, "white-space:nowrap" works well across browsers.