Bundle: Unify bundling concepts (#950)

- Added ability to (re)generate sprite and bundle files on save.
- Added ability to update all sprites like bundle.
- Removed the button "Update image sprite" from context menu (saving sprite should regenerate it).
- Added observer, so changing any asset (ingredient) file or the recipe file would regenerate bundle.
- Refactored bundle code into smaller classes (like sprite)
- Bring harmony in both code bases.
- Bug fixes.
- Prone to regression (not sure). :D 

More details can be found https://github.com/madskristensen/WebEssentials2013/issues/950.