append background-image start

The idea here is to clearly separate the structure/styling:
By default, css-sprites requires us to add a class to the element(s), to apply the corresponding background-image.
What we want is a complete stylus mixin: just calling sprite(spriteName) will also apply background-image.
append remove flags for debugging purposes
header fixes
- sprites fix the path to the images
- update layout
- global tweaks
- require ui sprites
- update colors
header polyfills
sprite improvement moved to sprite task
sprite improvement clean and comment