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)
Merge pull request #2059 from adrexia/batch-actions

Batch actions styling