Refine tests for the data-* attribute

- Remove input-type-color.html that have been tested by html/semantics/forms/the-input-element/color.html.
- Merge data_unicode.html and data_unicode_attr.html
- Fix issues according to review comments
- Add page title and format codes

Signed-off-by: xiaojunwu <xiaojunx.a.wu@intel.com>