Bootstrap3 : font awesome icon cleanup (from H to O) + Change in ButtonGroup.java

Sorry to have put 2 different changes into one PR, but I don't know how to split them!

I've done Font Awesome icons cleanup (add, rename, remove) from letters H to O.

In ButtonGroup.java I've moved the call to the "newButtonList" in the "onInitialize" function.
So now when I override it, I can use properties that I cannot instantiate before the super() call.

My use case :

class RapportManifesteMenu extends ButtonGroup {
	private final PageReference backPage;

	public RapportManifesteMenu(final String varMarkupId, final PageReference varBackPage) {
		super(varMarkupId);
		backPage = varBackPage;
	}

	@Override
	protected List<AbstractLink> newButtons(final String varButtonMarkupId) {
		final List<AbstractLink> buttons = new ArrayList<>();
		buttons.add(new CancelLink(varButtonMarkupId, backPage, Model.of("Back"))); 
        }
}