Add event support

Add `.trigger()` calls to all 3 stages of the resizing process (start, resize, stop)

```js
column:resize:start // Passed [ $leftColumn, $rightColumn ]
column:resize // Passed [ $leftColumn, $rightColumn, newLeftWidths, newRightWidths ]
column:resize:stop // Passed [ $leftColumn, $rightColumn, newLeftWidths, newRightWidths ]
```