Adds support pattern without decimal separator in DecimalFormatter.

As requested in https://github.com/bartfeenstra/cldr/issues/1

The DecimalFormatterTest has been refactored to use PHPUnit's @dataProvider.

The test pattern for *No decimal separator* has been moved to *valid pattern* set and changed from 'foo' to 'fo0'.

The test for emtpy number has been changed to validate that the pattern contains at least one 0 (as specified in All formats should have one 0 before the decimal point (for example, avoid #,###.##)). This was required to ensure the pattern 'foo:bar' is considered empty. Previously, this pattern was considered invalid only because of the missing decimal separator.