treewide: HTML Cleanup

treewide: HTML Cleanup

* HTML Cleanup: Meta tags.
* Converted charset to shorthand.
* Removed meta tags with `Content-Script-Type` attribute. (Invalid in HTML5 spec.)

* HTML Cleanup: CSS tags.
* Removed `type` attribute with CSS files from link tags. (HTML5 spec recommends omitting it.)
* Removed `type` attribute from style tags. (Deprecated in HTML5 spec.)
https://html.spec.whatwg.org/#attr-link-type
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/style

* HTML Cleanup: Convert from XHTML to HTML5
* Removed XML declaration.
* Removed XML namespace.
* Changed doctype to HTML5.

* HTML Cleanup: CDATA tags.
* CDATA sections should not be used within HTML they are considered as comments and not displayed.
https://developer.mozilla.org/en-US/docs/Web/API/CDATASection

* HTML Cleanup: Script tags.
* Removed `language` attribute from script tags. (No longer valid in HTML5)
* Removed `type` attribute with JavaScript MIME type from script tags. (HTML5 spec recommends omitting it.)
https://html.spec.whatwg.org/multipage/scripting.html#attr-script-type
https://mimesniff.spec.whatwg.org/#javascript-mime-type

Signed-off-by: Mustafa Can Elmacı <mustafacan@elmaci.net>