Make Split View Panes Resizable

1) Makes Split View Panes Resizable
2) Updates to the image cache buster (final piece to fix #6356)

@redmunds 
Up until now, `Resizer` module was only used to resize **panels**. With this change we're now using it for any **element**, so the terminology should be cleaned up. This includes the `panelResizeStart`, `panelResizeUpdate` and `panelResizeEnd` events which are used outside this module.