Fix errors in JavaFX API docs when using 'javadoc -html5'

Now that the JavaFX API docs are doclint clean we need to make them HTML5 compliant. We currently get 96 errors when using the '-html5' option of javadoc. Most of these are errors in our use of html tables. A few are places where we use deprecated tags, such as <tt>, which should be replaced with {@code}.

This should ideally be done before the JDK starts building HTML5 docs. See JDK-8175036.