Element::removeAttribute* does not need to throw
Merge pull request #2905 from brunoabinader/element-removeattr-no-throw

Element::removeAttribute* does not need to throw
Implement support for :disabled CSS selector
Implement support for :enabled CSS selector
Implement support for 'disabled' property in HTMLButtonElement
Implement support for 'disabled' property in HTMLFieldSetElement
Implement support for 'disabled' property in HTMLInputElement
Implement support for 'disabled' property in HTMLOptGroupElement
Implement support for 'disabled' property in HTMLOptionElement
Implement support for 'disabled' property in HTMLSelectElement
Implement support for 'disabled' property in HTMLTextAreaElement
Implement support for 'enabled' property in HTMLAnchorElement
Implement support for 'enabled' property in HTMLAreaElement
Implement support for 'enabled' property in HTMLLinkElement
Added HTMLButtonElement disabled content tests