Icons: Move images to sprite named folder
Icons: Use compass spriting

- Replace manual sprite with hash appended generated sprite
- base64 encode the sprite in modern browsers
- Fix relative/absolute path issue with Sass path using Ant task
Icons: Remove images duplicated from wb-icons

- Remove icons already included in the wb-icon folder
- Remove old manual sprite
Merge pull request #2376 from nschonni/use-compass-sprites

Use compass sprites