Make Split View Panes Resizable

1) Makes Split View Panes Resizable
2) Updates to the image cache buster (final piece to fix #6356)

@redmunds 
You made `POSITION_BOTTOM` and `POSITION_LEFT` public here, and are using them in MainViewManager.js, but I'm still seeing the following commented out blocks of code (which don't show up in this diff) in Resizer.js:

```js
//if ($(element).hasClass("bottom-resizer")) {
// makeResizable(element, DIRECTION_VERTICAL, POSITION_BOTTOM, DEFAULT_MIN_SIZE);
//}
```

```js
//if ($(element).hasClass("left-resizer")) {
// makeResizable(element, DIRECTION_HORIZONTAL, POSITION_LEFT, DEFAULT_MIN_SIZE);
//}
```

Should this code be enabled?