feat(config): always call the global `onLoad` handler

In my project, I wanted to setup Ace in the `uiAceConfig.ace.onLoad` handler because I was setting a lot of "advanced" options anyway. I then needed to configure hotkeys on individual Ace instances, which wiped out the global `onLoad` handler.

With this PR, the global `onLoad` handler is always called first followed by the instance `onLoad` if specified.