AjaxEventBehavior doesn't prevent the default behavior of the JavaScript event

"From now on only AjaxFallback** components prevent the default JavaScript event behavior so only the Ajax call is made when JavaScript is enabled in the browser. If the default behavior should be prevented in any use case then use: attributes.setPreventDefault(true)."
Impact: medium, requires careful testing. The default behavior should not matter but we may have to prevent it per-case when it does.