Batch actions styling

* Removed cog icon (usually associated with settings), and tidied up
padding (based on @clarkepaul's commit:
https://github.com/silverstripe-droptables/sapphire/commit/b09cd5f7f8e73
4df1f7ca0d387a5b97a03a3b604)

Before:
![4_06_13_12_40_pm](https://f.cloud.github.com/assets/984753/603059/b67d650a-ccb0-11e2-8f85-f18a8c4a51ab.png)
![filter-old-down](https://f.cloud.github.com/assets/984753/603060/c00fc9dc-ccb0-11e2-83dc-fa632b0b00c3.png)


After:
![4_06_13_12_38_pm](https://f.cloud.github.com/assets/984753/603062/c9d86fd2-ccb0-11e2-920c-43e08166aee9.png)
![filter-new-down](https://f.cloud.github.com/assets/984753/603064/cd4e5e4c-ccb0-11e2-831c-54e83752f7db.png)