API Default to "yyyy-MM-dd" for date format

[chillu]

The motivation for this was to avoid using "MMM" in particular, since it causes inconsistencies in month
names between jQuery UI and Zend_Locale_Format.
One example of that was "mar." (jQuery UI( vs. "mars" (Zend_Locale) as a danish short month name.

This means if you set a default locale of de_DE for example,
the date format will still be yyyy-MM-dd (rather than dd.MM.yyyy).
You still get that one as a suggestion in the member profile,
and can set it as a global default through i18n.date_format config API,
its just not auto detected any longer. This also makes i18n::get_date_format()
obsolete, since we can now simply use the Config API without any dynamic calls.

I've implemented the same changes for consistency in time_format as well.

Fixes silverstripe/silverstripe-cms#544

[halkyon]

I've merged in fixes for PHPUnit from 3.1 branch so Travis should work on pull requests against master now.

Anyway, there's some failures in the current tests. I've cherry picked the commit from this pull onto the latest HEAD of master, ran the tests and got these failures:

1. MemberDatetimeOptionsetFieldTest::testDateFormatDefaultCheckedInFormField
   Failed asserting that two strings are equal.
   --- Expected
   +++ Actual
   @@ @@
   -'checked'
   +''

/Users/sharvey/Sites/ssmaster-dev/framework/tests/forms/MemberDatetimeOptionsetFieldTest.php:52
/Users/sharvey/.composer/vendor/phpunit/phpunit/composer/bin/phpunit:63

2. i18nTest::testDateFormatFromLocale
   Failed asserting that null matches expected 'MMM d, y'.

/Users/sharvey/Sites/ssmaster-dev/framework/tests/i18n/i18nTest.php:70
/Users/sharvey/.composer/vendor/phpunit/phpunit/composer/bin/phpunit:63

3. i18nTest::testDateFormatCustom
   Failed asserting that null matches expected 'MMM d, y'.

/Users/sharvey/Sites/ssmaster-dev/framework/tests/i18n/i18nTest.php:86
/Users/sharvey/.composer/vendor/phpunit/phpunit/composer/bin/phpunit:63

4. MemberTest::testMemberWithNoDateFormatFallsbackToGlobalLocaleDefaultFormat
   Failed asserting that null matches expected 'MMM d, y'.

/Users/sharvey/Sites/ssmaster-dev/framework/tests/security/MemberTest.php:324
/Users/sharvey/.composer/vendor/phpunit/phpunit/composer/bin/phpunit:63

5. MemberTest::testMemberWithNoDateFormatFallsbackToTheirLocaleDefaultFormat
   Failed asserting that null matches expected 'dd.MM.yyyy'.

/Users/sharvey/Sites/ssmaster-dev/framework/tests/security/MemberTest.php:330
/Users/sharvey/.composer/vendor/phpunit/phpunit/composer/bin/phpunit:63

[chillu]

Thanks for reviewing, Sean! Builds should be passing now, sorry for that mess. I've applied the same changes to time_format, and rejiggered the code a bit - would you mind having another look?