WIP - Add cache busting

Waiting for AsseticBundle 2.4 & Assetic 1.2 to be released

```
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for symfony/assetic-bundle dev-master -> satisfiable by symfony/assetic-bundle[dev-master].
    - symfony/assetic-bundle dev-master requires kriswallsmith/assetic ~1.2 -> no matching package found.
```