(Follow-up to #17) Using coffee-maven-plugin for coffee script compilation

* Removing call to CoffeeScript processor
* Using maven-executor to call coffee-maven-plugin
* **CHANGE** : As coffee-maven-plugin don't respect hierarchy in the target directory (or I didn't find the option) files are now all on the same level. For aggregation, don't add directory hierarchy (or we'll have to take that into account)

Signed-off-by: nicolas-rempulski <nicolas.rempulski@gmail.com>