Make Split View Panes Resizable

1) Makes Split View Panes Resizable
2) Updates to the image cache buster (final piece to fix #6356)

@redmunds 
Those are for elements which are made resizable by virtue of having a special selector in html content.  There aren't any that I know of so this would have no impact on the functionality of brackets.  

However, I'm not sure why the code was commented out. IIRC, the initial implementation didn't work or didn't have this feature so it was either commented out or it the functionality was added later along with the code commented out because it wasn't needed.

If we want to enable elements to get a resizer from the bottom or right in the `index.html` then we would need to enable this.

I'm indifferent to it.  Since it isn't being used it isn't being tested.  BTW -- The brackets-outline uses "left".  There are still no uses of "bottom" other than SplitView.