JBIDE-16687 provide access to palette entries via content assist
JBIDE-17154 HTML5 Version Popup Window wrong placement

Updated in order to take into account palette scroll
JBIDE-17156 Palette wizards of HTML category should not have 'Add js/css' checkbox
Inheritance of Palette wizard is changed so that super class has only
functionalyty common for all widgets, while specific of jQuery and HTML
is moved to subclasses.