Merge pull request #3 from chadrien/master

Composer should not install dev requirements
Added copy_exclude to magento recipe
Added composer and modman specific recipes
Fixed default value for copy_exclude

... so it does not throw errors when empty initially
Use copy strategy for modman to prevent messing up with relative symlinks

... in case the deployment recipe has to move them around after the deployment
for instance if the directory has to be moved in a shared location
Re-enable composer scipts

Why should composer scripts(or callbacks) should be disabled? I don't
see any good reasons to it.