Added loading and disabled user feedback on batch actions button for cms...

https://github.com/silverstripe/silverstripe-cms/issues/441

Added images to "Go" .Action:submit button for ui-state-disabled -focus, -active and -default.

Added existing "Throbber.gif" for ui-state-focus and -active to show the batch actions as "working".

Also used existing icons for disabled and active states for better user feedback.

IE wouldn't clear ui-state-focus so had to force this in JavaScript LeftAndMain.BatchActions.js.

Safari and Firefox replace ui-state-focus with ui-state-active - so added additional CSS to account for this.

Before fix:

![oldbatchactionsactive](https://cloud.githubusercontent.com/assets/2508506/4802458/75e3922c-5e44-11e4-8355-76ff4a6ba9b4.png)
![oldbatchactionsdisabled](https://cloud.githubusercontent.com/assets/2508506/4802459/75e721a8-5e44-11e4-841b-81e80af10d83.png)


After Fix:

![batchactionsthrobber](https://cloud.githubusercontent.com/assets/2508506/4802755/e247888c-5e4a-11e4-9f90-667a4ff4ef66.jpg)
![batchactionsactive](https://cloud.githubusercontent.com/assets/2508506/4802464/80f3c1b4-5e44-11e4-9e1f-5fe52eaf0238.png)
![batchactionsdisabled](https://cloud.githubusercontent.com/assets/2508506/4802466/80fcfe64-5e44-11e4-894b-3514b7c88c29.png)