Twenty Eleven: Add theme support for HTML5

[poena]

By proactively adding theme support for HTML5 and fixing any styling issues,
we can prevent problems if the HTML5 theme support becomes the default for all themes.

But not least, it updates the markup to more modern standards.

Without HTML5 support enabled, the comment form in Twenty Eleven uses the text input field for the email input.

With HTML5 support enabled, the comment form is switched to using the email input field, and this changes the positioning of the field, breaking the layout.

Related to #61183
Follow up to #20579

[poena]

Twenty Eleven with HTML5 theme support

[sabernhardt]

adds full array of HTML5 supports and fixes the comment form input types

[sabernhardt]

I uploaded a patch to test more elements.

In addition to the comment form input fields:

• the gallery shortcode output would lose the column grid
• the caption shortcode would change its width (possibly only a minor difference)

The classic navigation widgets looked the same with the nav element at first glance: Archives, Categories, Meta, Navigation Menu, Pages, Recent Comments, Recent Posts, RSS and Tag Cloud. For the search form, Twenty Eleven has its own searchform.php template.

Child themes that replace the main stylesheet would need to update their styles if the theme support is added (unless the theme also overrides the twentyeleven_setup() function or the site does not enable comments).

I think it would be worth at least adding the two input types in the stylesheet for the comment form, even if the support is not officially added in twentyeleven_setup().

[karmatosed]

I am really torn on this one. On one hand I like the idea of a little future proofing but what don't find sits so well considering we don't know what doing with these themes is the following:

Child themes that replace the main stylesheet would need to update their styles if the theme support is added (unless the theme also overrides the twentyeleven_setup() function or the site does not enable comments).

I would absolutely be up for a passive enhancement if that was at all possible without that @sabernhardt.