Prefix event name for modals and tooltips

This feature changes the events namespace from using `options.prefixClass` to `options.prefixEvent`. I found the need for this when I had multiple modals on the same page and wanted to do some tasks on the `hide` event. Using `options.prefixClass` also changes the classes so I couldn't continue to use the default styling, adding this option allowed me to watch for the hide event for specific modals only.

There's also a small bugfix for when tipElement was set to null.