fix(message): use locale-aware time formatting in IMP_Message_Date (#22)

[jcdelepine]

Title: fix(message): use locale-aware time formatting in IMP_Message_Date (#22)

Description:

IMP_Message_Date::_format() passed the preference value directly to Horde\Date\Format::formatDate(). When time_format or time_format_mini held a named ICU style ('medium', 'short'), formatDate() formatted the date portion instead of the time portion, resulting in dates being displayed where times were expected.

Fix by using Horde\Date\Format::TIME_ONLY for time preferences:

if (in_array($type, ['time_format', 'time_format_mini'], true)) {
    return ltrim(Horde\Date\Format::formatDate((int) $udate, $GLOBALS['prefs']->getValue($type), $GLOBALS['language'] ?? 'en_US', Horde\Date\Format::TIME_ONLY));
}
return ltrim(Horde\Date\Format::formatDate((int) $udate, $GLOBALS['prefs']->getValue($type), $GLOBALS['language'] ?? 'en_US'));

Depends on feat(format): add TIME_ONLY constant and parameter to formatDate() : horde/Date#19.
@ralflang FYI.