Start updating HtmlHelper to use string templates.
Finish updating HtmlHelper methods to use string templates.
Remove protected methods that no longer have callers.

Remove duplicated code from Helper that is now available in
StringTemplate, and the StringTemplateTrait.
Fix failing test.
Fix lint error.
Remove type attributes from script and link tags.

They are optional in HTML5 which is going to be the default doctype for
3.0
Remove old _tags property and useTag() method.

Both of these are not really that useful. useTag can be replaced with
tag(), I'm not really sure why we ever had both.
Remove default type attribute from style tag as well.

It is not needed in HTML5.
Add missing option.
Merge pull request #2968 from markstory/3.0-html-helper

3.0 Update HTML helper
Improve docblock formatting.